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Retirement · Updated July 20, 2026

California §401(k) and IRA Basis in 2026: Federal Conformity, Community Property, and the 13.3% Top Rate

California is a federal-conforming state for §401(k) elective deferrals and IRA basis, but a 12.3% top marginal rate stacked with the 1% Behavioral Health Services Tax, a strict Franchise Tax Board residency regime, and a community property regime that reaches through Roth IRA titling change nearly every retirement-account decision a Californian makes. This is the 2026 field guide.

CalcLeap Editorial Published July 20, 2026 19 min read How we research

Our Pennsylvania §401(k) after-tax basis field guide from July 17 established the framework for state-by-state deviations from federal §401(k) treatment. California sits at the opposite end of that framework: rather than diverging from federal treatment through a contribution-point taxation rule the way Pennsylvania does, California explicitly conforms to Internal Revenue Code §401 under Revenue and Taxation Code §17501, and to IRC §§402, 408, and 408A under the same automatic-conformity language. That conformity is broad enough that most of what California residents need to know about §401(k) and IRA basis matches the federal treatment exactly — no distinct state basis, no separate California basis form, no contribution-point taxation problem.

What California adds is not a divergence at the basis layer but a divergence at nearly every adjacent layer: the highest state marginal income tax rate in the United States at 12.3 percent, stacked with the 1 percent Behavioral Health Services Tax surtax at income above $1,000,000; the strictest state residency regime in the country enforced by the Franchise Tax Board through the residency framework in Franchise Tax Board Publication 1031 and the multi-factor Bragg-based residency analysis; a community property regime under California Family Code §760 that overrides federal titling for divorce, testamentary passage, and creditor purposes even where IRC §408(g) preserves the federal single-owner treatment of IRAs; and a specified conformity date of January 1, 2015 that leaves large swaths of the SECURE Act, SECURE 2.0, and OBBBA outside California's automatic conformity — meaning California may or may not follow each specific federal change and taxpayers must check.[1]

The practical planning implications are large. A California resident earning $340,000 who defers $23,500 into a §401(k) captures a $2,890.50 California state tax deduction (12.3% × $23,500 at the top marginal bracket applying at this income) that a Pennsylvania resident at similar income would not — this is federal conformity working in the Californian's favor. But the same California resident planning a Roth conversion at retirement pays California state tax on the conversion at the marginal rate unless they relocate before the conversion year, and the differential between a California-resident conversion and a Nevada-resident conversion at the top bracket approaches 13.3 cents on every incremental dollar converted. This guide walks the whole picture: the R&TC §17501 automatic-conformity provision and its perimeter, the specified conformity date and its practical effect on SECURE Act provisions, the community property mechanics that overlay Roth IRA titling, the FTB residency framework, the interaction with SECURE 2.0 §603 mandatory Roth catch-up, three worked case studies at $150,000 San Francisco / $340,000 Los Angeles / $620,000 California-to-Nevada relocation, six California-specific mistakes to avoid, and an 8-item action checklist. Model the base §401(k) mechanics using the 401(k) calculator, the marginal-rate stacking using the income tax calculator, and the retirement drawdown modeling using the retirement calculator.

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1. R&TC §17501 and California's federal conformity to §401(k) and IRA rules

California Revenue and Taxation Code §17501 provides automatic conformity to federal law on qualified retirement plans. The provision reads that Part I of Subchapter D of Chapter 1 of Subtitle A of the Internal Revenue Code — the sections governing pension, profit-sharing, and stock bonus plans — apply for California purposes. Because §17501 uses automatic-conformity language rather than a specified date, changes to IRC §401 and the surrounding sections apply for California without a separate California statute unless the California Legislature affirmatively acts to decouple.[2] Part I of Subchapter D includes IRC §401 (qualified plan requirements), §402 (taxation of beneficiaries of employees' trusts), §408 (individual retirement accounts), §408A (Roth IRAs), and the surrounding provisions that define contribution limits, deduction rules, distribution rules, and basis rules.

The practical effect is that the 2026 IRS Notice 2025-67 retirement plan limits apply for California without any Legislative action. The 2026 §401(k) elective deferral limit of $24,500, the age-50 catch-up of $8,000, the age-60 through 63 super catch-up of $11,250 added by SECURE 2.0 §109, the IRC §415(c) annual additions ceiling of $72,000, the IRA contribution limit of $7,500 base with an $8,600 age-50 catch-up, and the Roth IRA MAGI phaseouts of $153,000 to $168,000 single and $242,000 to $252,000 MFJ are all California-effective automatically.[3] A California-resident participant deferring $24,500 into a §401(k) in 2026 excludes the full deferral from both Box 1 federal wages and California state wages on Form W-2.

Basis rules conform identically. A California resident who makes a nondeductible Traditional IRA contribution files federal Form 8606, and the resulting basis figure is the California basis figure — there is no separate California Form 8606-CA, and the California return simply follows the federal basis calculation.[4] IRC §408(d)(2) pro-rata rule for distributions from Traditional IRAs applies for California with no state-level modification. IRC §408A(c)(2) Roth IRA basis rules — that contributions constitute basis recoverable at any time, that conversions constitute basis subject to the five-year recapture clock under §408A(d)(3)(F), and that earnings are the last dollar out under the ordering rules — all apply for California.

Same forms, same numbers, no California overlay

Because R&TC §17501 automatically conforms California to IRC §§401, 402, 408, and 408A, California residents do not file any separate California basis form or worksheet for §401(k) or IRA basis. Form 8606 filed with the federal return is dispositive for California too, provided California residency was maintained during the years in question.

2. Where California diverges: the January 1, 2015 specified conformity date

Outside the §17501 automatic-conformity perimeter, California conforms to the Internal Revenue Code as of a specified date — currently January 1, 2015 for most non-pension purposes.[5] Federal changes made after January 1, 2015 do not apply for California unless the California Legislature affirmatively passes a conformity statute. This has produced meaningful divergence between California and federal treatment on several post-2015 retirement-related provisions:

  • SECURE Act (December 20, 2019). The SECURE Act made changes across many provisions of the Code, including some inside the §17501 perimeter (which conform automatically for California) and some outside it (which do not conform unless California acts). The change to §401(a)(9) required beginning date (age 72 for §401(a)(9)) is inside §401 and therefore conforms; the addition of §401(a)(9)(H) (the 10-year post-death payout rule) is inside §401 and therefore conforms; the change to §529(c)(3)(E) allowing §529 plan rollovers into Roth IRAs is inside §529 which is outside the §17501 perimeter and therefore does not automatically conform.
  • SECURE 2.0 (December 29, 2022). Same layer-by-layer analysis. §603 mandatory Roth catch-up under §414(v)(7) is inside §414 which is inside Part I of Subchapter D and therefore conforms; §325 elimination of lifetime RMDs for Roth §401(k) accounts under §401(a)(9)(H) is inside §401 and therefore conforms; §604 optional Roth employer contributions under §402A(c)(4)(D) is inside §402A which is inside Subchapter D and therefore conforms.
  • OBBBA (2025). Most OBBBA provisions relating to retirement plans that amend §§401 through 415 conform automatically; provisions amending §§529, 530, or 72 outside the §17501 perimeter require California legislative action.

The pattern to watch: anything the federal change amends inside Part I of Subchapter D of Chapter 1 of Subtitle A (roughly IRC §§401-425) conforms automatically for California. Anything the change amends in §529, §530, §72, §1411 (NIIT), or elsewhere requires separate California conformity legislation. Before assuming a specific SECURE Act, SECURE 2.0, or OBBBA provision applies for California, check the current Franchise Tax Board Summary of Federal Income Tax Changes report, which the FTB publishes annually and updates for each federal act.[6]

3. Community property mechanics and Roth IRA titling

California is one of nine community property states in the United States (Arizona, California, Idaho, Louisiana, Nevada, New Mexico, Texas, Washington, and Wisconsin). Under California Family Code §760, all property acquired by either spouse during marriage, while domiciled in California, is community property — meaning it is owned by both spouses in equal, undivided one-half shares regardless of which spouse's name appears on the title.[7] Family Code §770 defines separate property as property owned before marriage, acquired by gift or inheritance during marriage, or acquired with the rents or profits of separate property; Family Code §751 provides that spouses have equal management and control of community property.

Wages earned during marriage while a California resident are community property. Contributions to §401(k) accounts and IRAs made from those wages are community property. The growth on those contributions attributable to the community property principal is community property. This has consequences for divorce (assets are divided 50/50 without regard to titling), for testamentary passage (the surviving spouse takes half automatically under Cal. Probate Code §100, and the deceased spouse can devise only their community half), and for creditor reach (community property is reachable for community debts of either spouse under Family Code §910).

But for federal income tax purposes, IRC §408(g) explicitly overrides community property law for IRAs. It provides that an IRA "shall be determined without regard to any community property laws." This means for federal income tax reporting — Form 1099-R issuance, Form 5498 reporting, the annual contribution limit under IRC §408(a)(1) — the IRA is treated as the property of the named account owner alone, and community property law does not split the account 50/50 for tax purposes. The named account owner reports all IRA income on their return regardless of California community property law.[8]

Where community property law matters for California retirement account planning:

  • Divorce division. §401(k) accounts are divided by Qualified Domestic Relations Order under Cal. Fam. Code §2610; IRAs are divided by transfer incident to divorce under IRC §408(d)(6). The 50/50 California community property presumption applies unless the parties agree otherwise or trace to separate-property funding.
  • MFS filing. When California-resident spouses file Married Filing Separately, they must split community property income 50/50 on each return under California's community property income splitting rules. This includes W-2 wages (which are split for California even though the federal MFS return follows federal community property splitting rules for federal purposes too). The result is that each MFS filer reports one-half of the couple's combined wages, which can push a substantially-lower-earning spouse above the $10,000 MFS Roth IRA MAGI phaseout under IRC §408A(c)(3)(B)(i) — a real trap for California MFS filers hoping to preserve Roth eligibility.
  • Basis tracking on inherited IRAs. A California-resident spouse who inherits a community property IRA takes a §1014 basis step-up on the community half of the account (both halves under Cal. Rev. & Tax. Code §17400 conformity to federal §1014(b)(6) community property step-up), which is generally irrelevant for the retirement account itself since retirement accounts are IRD (income in respect of a decedent) not eligible for §1014 step-up under §1014(c) — but the community property mechanic does affect the basis in appreciated assets held outside retirement accounts.

Community property applies at CA-residency time — not before or after

Community property under Cal. Fam. Code §760 attaches only to property acquired while the couple is domiciled in California. A couple moving to California from Texas (also community property) generally preserves the community characterization of pre-move assets; a couple moving from Ohio (a common-law state) generally treats pre-move assets as separate property unless the couple executes a transmutation agreement under Fam. Code §852. Consult a California family law attorney before assuming pre-move retirement assets are automatically community property.

4. The 12.3% top rate and the 1% Behavioral Health Services Tax

California's Personal Income Tax Law at R&TC §17041 imposes a graduated income tax on residents at rates from 1% to 12.3% across nine brackets, indexed annually for California-specific inflation.[9] The 12.3% top marginal rate applies to taxable income above roughly $721,000 single for 2025 (the last-published year's brackets, with 2026 brackets to be published by the Franchise Tax Board later in 2026 with the standard inflation adjustment). On top of the 12.3% rate, R&TC §17043 imposes an additional 1% Mental Health Services Tax — renamed the Behavioral Health Services Tax by Proposition 1 passed by California voters in March 2024 — on California taxable income above $1,000,000 regardless of filing status.[10]

The $1,000,000 threshold under R&TC §17043 does not double for MFJ filers. A single filer above $1,000,000 pays the 1% surtax; a MFJ couple above $1,000,000 combined pays the 1% surtax. This is a notable departure from most other California tax provisions and from most federal thresholds, and it means the surtax bites harder at MFJ couples where each spouse is well below the surtax threshold individually.

2026 California Marginal Rate (Illustrative)Federal Marginal RateCombined Marginal
1% (lowest bracket, ~$0-$11,000 single)10%11%
6% (mid-income, ~$40,000-$60,000 single)22%28%
9.3% (upper-middle, ~$70,000-$375,000 single)24-35%33.3%-44.3%
10.3% (~$375,000-$450,000 single)35%45.3%
11.3% (~$450,000-$721,000 single)35%46.3%
12.3% (~$721,000-$1,000,000 single)37%49.3%
13.3% (above $1,000,000 single, includes 1% BHSA)37% + 0.9% Add'l Medicare51.2% (before NIIT)

The retirement-planning implication of the surtax is that Traditional §401(k) contributions that reduce California taxable income from above $1,000,000 to below $1,000,000 save the full 13.3% marginal rate rather than the 12.3% headline rate. A $23,500 elective deferral for a participant in the surtax band produces $3,125.50 of California state tax savings alone (13.3% × $23,500) — larger than the state tax savings at any other bracket. Conversely, a Roth conversion that pushes California taxable income above $1,000,000 pays the full 13.3% on the incremental amount. For high-income California residents at the surtax threshold, the Traditional-vs-Roth 401(k) decision has an unusually strong pretax tilt driven purely by the state-tax component of the analysis.

5. Roth conversion in California — cost, timing, and the relocation window

A Roth conversion under IRC §408A(d)(3) is a taxable transfer of a Traditional IRA (or a Traditional §401(k) source) into a Roth IRA (or a designated Roth §401(k) source). The amount converted is included in gross income in the conversion year, taxed at ordinary rates federally, and taxed at California's ordinary rates for California residents in the conversion year. The Franchise Tax Board treats conversions the same as the IRS: the converted amount goes on line 1a of the California return as retirement plan income, with the taxable portion computed identically to the federal Form 8606 calculation.[11]

For a California resident, the marginal cost of the conversion is the sum of federal marginal, California marginal (up to 12.3% or 13.3% with BHSA), and any spillover NIIT or IRMAA effects the additional income triggers. At the top brackets, this can reach roughly 51-52% combined marginal for California residents in the surtax band — the highest combined-marginal Roth conversion cost of any U.S. residency.

Two planning strategies flow from this. First, for participants who expect to retire in California, the state-tax cost of the conversion is baked in regardless of timing — the participant will pay California marginal rates at conversion, and would have paid California marginal rates on the eventual Traditional distribution instead. The pure-state math is close to neutral for a permanent California resident because the state rate structure at retirement income levels (typically $60,000-$180,000 for retirees) is similar to the rate structure during peak working years (typically $150,000-$400,000 for professionals). The federal bracket-arbitrage question dominates.

Second, for participants who plan to relocate at or before retirement to a no-income-tax state — Nevada, Texas, Florida, Washington, Wyoming, South Dakota, Tennessee, New Hampshire (state I&D tax finished phaseout effective 1/1/2025), or Alaska — the state-tax cost of the conversion year is a live variable that shifts based on domicile. A $200,000 conversion executed in year 1 while a California resident costs approximately $24,600 in California state tax (12.3% × $200,000). The same conversion executed in year 2 after a clean relocation to Nevada costs $0 in state tax. That $24,600 savings is a real number that can shift the timing decision materially.

CA state tax on Roth conversion = converted amount × applicable CA marginal rate
$200,000 × 12.3% = $24,600 (at CA top marginal, pre-BHSA)
$200,000 × 13.3% = $26,600 (at CA top marginal, above $1M BHSA threshold)

Notes on the relocation window. The Pension Source Tax Act at 4 U.S.C. §114 protects former residents from source-state tax on periodic retirement distributions but does not protect against source-state tax on a Roth conversion, which is not a periodic distribution. The California residency test under Cal. Code Regs. Title 18 §17014 uses a facts-and-circumstances domicile analysis; the Bragg v. Franchise Tax Board factor list, developed by the Board of Equalization to guide the analysis, considers among other factors the state of the taxpayer's principal residence, driver's license, voter registration, vehicle registration, tax return filings, and days spent in each state.[12] The safest posture for a pre-conversion relocation is to complete the domicile-changing acts (physical move, driver's license, voter registration, vehicle registration, homestead exemption in the new state, filing a California nonresident final-year return with a Declaration of Nonresidency effective before the conversion date) before executing the conversion. Sequencing the conversion to occur in a full nonresident year is the cleanest audit defense.

6. The Pension Source Tax Act — §114 protection when leaving California

The Pension Source Tax Act of 1996, enacted as Public Law 104-95 and codified at 4 U.S.C. §114, prohibits any state from imposing an income tax on the retirement income of an individual who is not a resident or domiciliary of that state at the time the retirement income is paid. The protected categories of retirement income are enumerated in §114(b)(1) and include:

  • Distributions from IRC §401(a) qualified retirement plans (including §401(k) plans)
  • Distributions from IRC §403(a) qualified annuity plans
  • Distributions from IRC §403(b) annuities and custodial accounts
  • Distributions from IRC §408 IRAs and IRC §408A Roth IRAs
  • Distributions from IRC §457 governmental plans and eligible §457(b) plans
  • Distributions from IRC §414(d) governmental plans
  • Nonqualified deferred compensation from IRC §3121(v)(2)(C) plans if paid as substantially equal periodic payments over the life or life expectancy of the recipient (or the recipient and their designated beneficiary), or over a period of at least 10 years

For a former California resident who has completed a clean domicile change to Nevada, Florida, Texas, or any other state, California cannot impose income tax on the categories of retirement income listed above regardless of the fact that the underlying contributions were made while a California resident.[13] This is a strong shield — the categories cover essentially every mainstream retirement account type. The dollars flowing out of a §401(k), IRA, Roth IRA, or governmental §457(b) in retirement escape California income tax if paid after the domicile change, without regard to how much of the underlying balance was funded through California-taxed contributions.

Two important qualifiers. First, §114 does not protect against California tax on income accrued while a resident and paid after relocation that is not a §114-listed retirement distribution — including lump-sum distributions from nonqualified deferred compensation not meeting the 10-year-or-life periodic-payment safe harbor, and incentive stock option exercise gains attributable to California-performed services. Second, §114 does not exempt the former resident from the California residency test — California can still challenge the residency change, and if it prevails, the entire year of income is subject to California tax as a resident return. The §114 shield is only as strong as the underlying domicile change.

7. California residency, FTB Publication 1031, and the Bragg factors

California's residency framework is unusually strict compared to most other states. Cal. Rev. & Tax. Code §17014 defines a resident as any individual who is either domiciled in California or physically present in California for more than 9 months of the taxable year (the 9-month presumption is rebuttable). Domicile is a facts-and-circumstances determination — the state of the taxpayer's "true, fixed, and permanent home" to which the taxpayer intends to return whenever absent.[14]

The Franchise Tax Board issues Publication 1031 "Guidelines for Determining Resident Status" summarizing the domicile analysis and the multi-factor test for closest connection.[15] The Board of Equalization's decision in In re Bragg (State Board of Equalization, 2003) sets out a widely-cited 15-factor list the FTB uses in residency audits:

  • Amount of time spent in California versus elsewhere
  • Location of the taxpayer's spouse and children
  • Location of the taxpayer's principal residence
  • State of driver's license issuance
  • State of vehicle registration
  • State of voter registration and voting record
  • Location of bank accounts and safe deposit boxes
  • Location of professional licenses and memberships
  • Location of doctors, dentists, and other medical providers
  • Location of place of employment or business
  • Location of social ties (churches, clubs, gyms)
  • Location of real property ownership
  • Filing status on tax returns (resident vs nonresident)
  • Location of registered domestic partnership
  • Address on federal tax returns and other federal filings

The Bragg factors are not scored mathematically; the FTB and the Office of Tax Appeals weigh them holistically. A relocation from California to Nevada that changes only the physical address and California driver's license — while leaving the taxpayer's spouse, medical providers, family home, and business ties in California — will not withstand a residency audit and will likely result in California maintaining resident-status treatment. A relocation that changes physical address, driver's license, voter registration, vehicle registration, homestead exemption, spouse and family relocation, medical providers, professional memberships, and social ties will generally withstand audit even if the taxpayer maintains an investment property or a family visit pattern in California.

The 546-day safe harbor for California-employer employees

R&TC §17014(d) provides a safe harbor for California residents employed outside the state under a long-term employment contract of at least 546 consecutive days — the taxpayer is treated as a nonresident for the days outside California even if California remains their state of domicile. This safe harbor is narrow but well-defined; it applies primarily to expatriate assignments and does not cover ordinary domestic relocations for retirement.

8. Mega backdoor Roth mechanics for California residents

The mega backdoor Roth strategy — after-tax employee contributions to a §401(k), followed by an in-plan Roth rollover under IRC §402A(c)(4)(E) or an in-service withdrawal under IRC §402(c)(2) — works for California residents identically to how it works for residents of any other state, because both the after-tax contribution rules under IRC §401(m)(2) and the in-plan Roth rollover rules under IRC §402A are inside the §17501 automatic-conformity perimeter.[16] California conforms.

The mechanics for a California resident:

  1. The participant contributes the pre-tax elective deferral of $24,500 in 2026, capturing the California state tax deduction at their marginal rate (up to 13.3%).
  2. The employer contributes matching and nonelective contributions, which are excluded from California wages the same way they are excluded from federal wages at the contribution point.
  3. The participant makes voluntary after-tax contributions to the plan up to the IRC §415(c) annual additions ceiling of $72,000 — the after-tax portion equals $72,000 minus the elective deferral minus the employer contribution. For a participant with a $10,000 employer match and a $24,500 elective deferral, the mega backdoor capacity is $37,500. The after-tax contribution is made from already-federal-taxed and already-California-taxed dollars.
  4. The participant elects an in-plan Roth rollover of the after-tax source, either automatically on a same-day basis (Fidelity, Empower, and Schwab all offer this) or through a periodic conversion election. The rollover itself is not a federal or California taxable event to the extent it represents recovery of basis under IRC §72(d); any earnings that have accumulated between contribution and rollover are taxable ordinary income both federally and for California.

The California-specific consideration is the interaction with the 13.3% top marginal rate on any earnings converted. Because the pre-Roth-rollover earnings on the after-tax source are ordinary income at conversion, a delay in executing the in-plan rollover exposes those earnings to California marginal tax. Same-day automatic conversion eliminates the exposure. Most California participants at large-employer plans (Google, Meta, Apple, Salesforce, Netflix, Nvidia — all of which offer the mega backdoor strategy) use the same-day automatic conversion sweep to eliminate this exposure entirely.

9. SECURE 2.0 §603 mandatory Roth catch-up in California

Our SECURE 2.0 §603 field guide from July 11 covers the mechanics in detail. The California-specific overlay: because IRC §414 is inside the §17501 automatic-conformity perimeter, the §414(v)(7) mandatory Roth catch-up rule enacted by SECURE 2.0 §603 applies for California without any separate conformity action. Starting January 1, 2026, a California-resident participant whose 2025 Social Security wages from the same-employer sponsor exceeded $150,000 must make all age-50 and age-60-through-63 catch-up contributions to that plan as designated Roth contributions rather than as pretax elective deferrals.[17]

The California state-tax consequence is meaningful. Before §603, a §603-covered California participant could shelter $8,000 of age-50 catch-up plus $11,250 of age-60-through-63 super catch-up ($19,250 total for a participant age 60-63) from both federal and California income tax. Starting in 2026, the same participant loses the California state-tax deferral on that $19,250 — at the 12.3% marginal California rate, the immediate additional California tax cost is $2,367.75; at the 13.3% marginal rate (including the BHSA surtax), the immediate additional California tax cost is $2,560.25. This is on top of the federal tax cost of the mandatory Roth treatment, which for a participant in the 32% federal bracket is $6,160 on the $19,250.

Because California has the highest state marginal rate in the country, the state-tax cost of §603 for California-resident high-earners is larger than for participants in any other state. The federal-analysis of Roth-vs-pretax remains the same; the state-tax cost is simply larger in California. For California residents whose federal analysis marginally favors pretax, §603 costs them meaningfully more than the same participant would lose in Ohio (4% state rate — cost $770), Illinois (4.95% cost $953), or Texas (0% cost $0).

10. Three worked case studies

Case A — Priya, $150,000 San Francisco software engineer, age 42

Priya is a single filer earning $150,000 base salary at a San Francisco tech company. Her California marginal rate at $150,000 taxable income is 9.3% (2025 brackets; 2026 brackets similar with FTB inflation adjustment). Her federal marginal rate is 24%. Combined marginal 33.3%. She has no §603 exposure — her 2025 Box 3 wages were $150,000, below the $150,000 §603 threshold (technically at the threshold; §603 applies only above $150,000, so she is exempt for 2026). She contributes the full $24,500 elective deferral pre-tax, capturing federal tax savings of $5,880 and California tax savings of $2,278.50 for a combined tax value of $8,158.50 on the $24,500 deferral.

Priya also makes after-tax mega backdoor Roth contributions of $30,000 (her employer match is $7,500 + her $24,500 deferral = $32,000 elective + match, leaving $40,000 of §415(c) headroom — she contributes $30,000 to preserve some headroom for future matches). The $30,000 mega backdoor contribution is made from after-tax dollars, so it does not reduce California wages. Her plan (offered through Fidelity NetBenefits) sweeps the after-tax source to Roth on a daily basis, so no earnings accumulate before conversion. She has no additional California tax on the mega backdoor conversion.

Total 2026 Roth accumulation: $30,000 mega backdoor plus $7,500 direct Roth IRA (she is under the $153,000 MAGI phaseout threshold for direct Roth IRA contributions as a single filer after the $24,500 deferral reduces her AGI below the threshold) = $37,500. Her Traditional §401(k) balance grows by $32,000 (deferral + match) plus market performance. Her marginal-rate arbitrage for the pretax portion is favorable given the near-certainty she will drop to a lower federal bracket in retirement.

Case B — Marcus, $340,000 Los Angeles physician, age 58, MFJ

Marcus is a physician in Los Angeles earning $340,000, filing MFJ with a spouse earning $110,000. Combined household California AGI approximately $450,000. Marcus's California marginal rate at that income is 11.3%; his federal marginal rate is 32%. Combined marginal 43.3%. He is §603-covered — his 2025 Box 3 wages of $340,000 well exceed the $150,000 threshold.

Marcus can defer the full $24,500 elective deferral pre-tax, capturing federal tax savings of $7,840 and California tax savings of $2,768.50 for a combined tax value of $10,608.50 on the $24,500. But his $8,000 age-50 catch-up under §603 must go into the Roth source. The immediate California tax cost of the §603 Roth treatment on the catch-up is $904 (11.3% × $8,000). The immediate federal tax cost is $2,560 (32% × $8,000). Total immediate tax cost on the catch-up: $3,464.

Marcus is weighing whether to do the catch-up at all given the forced Roth treatment. The break-even math: his projected retirement federal marginal is 22% (retirement income ~$140,000-$160,000), his projected retirement California marginal is 9.3% (if he stays in California) or 0% (if he relocates to Nevada). For a stay-in-California scenario, the retirement-year marginal is 31.3% combined vs the current-year marginal of 43.3% combined — pretax would have been mathematically favorable by 12 percentage points, but §603 forces Roth so he loses that 12-point spread on the $8,000 catch-up ($960 of value forgone). For a relocate-to-Nevada scenario, the retirement-year marginal is 22% (federal only) vs current 43.3% — pretax would have been favorable by 21.3 points, but §603 forces Roth so he loses $1,704 of value.

Marcus's decision: make the catch-up anyway because the forgone value ($960 to $1,704) is smaller than the value of the Roth being state-tax-free in retirement if he stays in California, and smaller than the value of the additional tax-free compounding runway. He also maxes his mega backdoor Roth capacity ($47,500 in his plan) and pays the ~$4,275 California tax on the after-tax portion (which is already after-tax California dollars, so no incremental California tax on the after-tax contribution itself — the $4,275 figure would be relevant only if there were significant earnings between contribution and Roth conversion, which same-day sweep eliminates).

Case C — Diana, $620,000 California-to-Nevada relocation, age 62, MFJ

Diana and her spouse David are relocating from Palo Alto to Reno effective January 2026. Diana's 2025 California income was $620,000; David's was $180,000; combined $800,000, well above the $1,000,000 threshold would trigger BHSA — they are below it. Combined California marginal rate 11.3%. Combined federal marginal rate 32%.

Diana has a $2.4M Traditional IRA (rolled over from a prior employer). She wants to execute a $300,000 Roth conversion. Timing analysis:

  • Conversion in 2025 as California residents: $300,000 × 32% federal = $96,000 + $300,000 × 11.3% California = $33,900 = $129,900 total tax. The conversion also pushes 2025 combined MFJ California AGI above $1,000,000 (from $800,000 to $1,100,000), triggering the BHSA surtax on the $100,000 above the threshold: additional 1% × $100,000 = $1,000. Total 2025 conversion tax: $130,900.
  • Conversion in 2026 as Nevada residents (post-relocation): $300,000 × 32% federal = $96,000. California tax on the conversion: $0 (Nevada resident by conversion date, and Roth conversions from IRAs are not California-source income for a nonresident under R&TC §17041(b)). BHSA does not apply outside California. Total 2026 conversion tax: $96,000.
  • California-tax savings from deferral: $130,900 - $96,000 = $34,900.

To claim the Nevada-resident treatment, Diana must complete a clean domicile change under the Bragg factors. Her execution plan: physically move December 15, 2025 (before year-end); California driver's license surrendered and Nevada driver's license issued January 5, 2026; California voter registration cancelled and Nevada voter registration completed January 15, 2026; California vehicle registration transferred to Nevada by February 1, 2026; Palo Alto home listed for sale in December 2025 and sold in Q1 2026; medical providers changed to Reno-based providers by March 2026; California return for 2025 filed as full-year California resident (correct), California return for 2026 filed as part-year California resident with California-source income only through the December 15, 2025 move date. The Roth conversion is executed in mid-2026 after the six-month domicile-establishment period has closed.

Total California tax savings from delaying the conversion: $34,900. Plus the additional $1,000 BHSA savings from not pushing 2025 income above the surtax threshold. Total savings: $35,900. The Pension Source Tax Act at 4 U.S.C. §114 then protects the subsequent Roth distributions in retirement from California tax indefinitely, so long as Diana remains a Nevada resident at the time of each distribution.

11. Six California-specific mistakes to avoid

1. Assuming California conforms to a specific SECURE 2.0 or OBBBA provision without checking. The §17501 automatic-conformity perimeter is narrower than most taxpayers assume — it covers §401 and adjacent pension provisions in Part I of Subchapter D, but not §529, §72, §408A(d) in some cases, or NIIT under §1411. Before assuming a specific federal change applies for California, verify against the current FTB Summary of Federal Income Tax Changes report.

2. Filing MFS with California-community-property income and losing Roth IRA eligibility. MFS filers in California must report half of the couple's community property W-2 wages on each MFS return, which can push a lower-earning spouse above the $10,000 MFS Roth IRA MAGI phaseout under IRC §408A(c)(3)(B)(i). If the couple is filing MFS specifically to preserve Roth IRA eligibility for one spouse, the community property income split typically defeats the strategy — the higher-earning spouse's wages are half-attributed to the lower-earning spouse's MFS return, pushing that spouse above the phaseout as well. Consult a California-tax-aware CPA before executing an MFS-based Roth planning strategy.

3. Executing a Roth conversion in a year of incomplete relocation. A conversion in a year the taxpayer is a part-year California resident is generally attributable in whole or in part to California under the Franchise Tax Board's part-year residency rules if the conversion date is before the effective relocation date, or if the FTB can establish that domicile remained in California through the conversion date. A conversion in a year the taxpayer files a full-year nonresident California return is generally not subject to California tax, but only if the domicile change under Bragg is defensible. Layer the conversion into the first full year of nonresidency, not the transition year.

4. Overlooking the BHSA $1,000,000 threshold for planning purposes. The 1% surtax under R&TC §17043 is often described as affecting "millionaires" without noting that the threshold applies at $1,000,000 California taxable income regardless of filing status. A MFJ couple at $950,000 combined California taxable income who executes a $100,000 Roth conversion in-state pays the 1% surtax on the $50,000 above the threshold — an easily-missed $500 marginal cost. Track combined taxable income against the threshold before executing any large one-year income event.

5. Confusing California R&TC §17501 automatic conformity with California specified-date conformity. The §17501 automatic-conformity language applies only to pension provisions in Part I of Subchapter D. Provisions in other parts of the Code — including many provisions that adjacent-touch retirement planning like §529, §1411, or §72(t) — conform to California only as of January 1, 2015 or by separate California conformity legislation. Assuming automatic conformity for a §529 change or a §1411 change is a common error.

6. Executing an in-plan Roth rollover of the after-tax source with accumulated earnings. Because IRC §72(d) allows recovery of after-tax basis before earnings on conversion, any earnings that accumulate between the after-tax contribution and the in-plan Roth rollover are ordinary income at conversion — including for California purposes at up to 13.3%. Same-day automatic conversion sweeps (offered by Fidelity, Empower, and Schwab at most large plans) eliminate the exposure. Manual periodic conversions (e.g., quarterly) allow earnings to accumulate and create a small but non-trivial California tax cost. For high-income Californians, the cost of a quarterly conversion cadence on a $30,000 after-tax contribution with 8% annual expected return is approximately $80-$300 of additional California tax per year vs same-day sweep.

12. 8-item pre-year-end action checklist for California residents

Actions to complete by December 31, 2026

  1. Max the §401(k) elective deferral to $24,500 (plus $8,000 age-50 catch-up if 50+, or $11,250 age-60-through-63 super catch-up if in that age band) — capture the full California state tax deduction at your marginal rate (up to 13.3% with BHSA).
  2. Verify §603 catch-up treatment for 2026. Check your 2025 Box 3 wages from your current-employer plan sponsor; if above $150,000, your 2026 catch-up must be Roth. Confirm the plan has adopted the required Roth source and the recordkeeper's §603 election flow before the year-end deferral election deadline.
  3. Execute the mega backdoor Roth strategy if your plan supports both after-tax contributions and in-plan Roth rollovers. Elect the same-day automatic conversion sweep to eliminate California tax on earnings between contribution and Roth conversion.
  4. File Form 8606 for any nondeductible Traditional IRA contribution. Track basis via the federal form; California accepts the federal basis without a separate California basis form.
  5. Review Roth conversion timing against any planned relocation. If relocating to a no-income-tax state, defer conversions until the first full year of nonresidency to capture the California state-tax savings (up to 13.3% on the converted amount).
  6. Track combined California taxable income against the $1,000,000 BHSA threshold. Time discretionary income events (Roth conversions, RSU vesting acceleration, deferred compensation payouts) to avoid crossing the threshold within a single year unless the crossing is unavoidable.
  7. Document the Bragg factors if planning a residency change. Assemble physical records — driver's license, voter registration, vehicle registration, homestead exemption, days-in-state calendar, spouse and family relocation documentation — before executing any post-relocation income event.
  8. Verify California conformity on any specific SECURE 2.0 or OBBBA provision your planning relies on. Check the current FTB Summary of Federal Income Tax Changes report before assuming California follows the federal treatment. Especially for §529 rollovers to Roth IRAs, §1411 NIIT, or any adjacent provision outside the §17501 perimeter.
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Frequently asked questions

Does California tax my 401(k) elective deferrals like Pennsylvania does?

No. California is a federal-conforming state for §401(k) elective deferrals under R&TC §17501. Your $24,500 deferral in 2026 is excluded from both federal and California wages in the year of contribution — you do not build a state-specific after-tax basis in the account. This is the opposite of Pennsylvania, which taxes deferrals at the contribution point under 72 P.S. §7301(d) and requires participants to track a distinct state basis.

What is R&TC §17501 and why does it matter?

Revenue and Taxation Code §17501 is California's automatic-conformity provision for qualified retirement plans. It provides that changes to IRC §401 and the surrounding pension provisions in Part I of Subchapter D of Chapter 1 of Subtitle A apply automatically for California, without a separate act of the California Legislature. This is why the 2026 IRS Notice 2025-67 $24,500 elective deferral limit, $72,000 §415(c) annual additions ceiling, and other 2026 retirement plan limits apply for California without waiting for California conformity legislation.

How does California's community property regime affect my Roth IRA?

California is one of nine community property states. Under Cal. Fam. Code §760, wages earned during marriage in California are community property in equal undivided one-half shares. IRC §408(g) explicitly overrides community property for federal income tax purposes — the IRA is treated as the individual property of the named account owner. But community property law still applies for divorce division, testamentary passage, and creditor reach. And for MFS filers, community property income splitting can push a lower-earning spouse above the $10,000 MFS Roth IRA MAGI phaseout.

Should I do a Roth conversion in California or wait until I move to Nevada?

If you are relocating to a no-income-tax state and the relocation is genuine and clean under California's Bragg residency framework, deferring the conversion until after the domicile change saves the full California marginal rate on the converted amount — up to 13.3% (12.3% + 1% BHSA) at the top bracket. On a $200,000 conversion, that is $24,600 to $26,600 of California state tax savings. The Pension Source Tax Act at 4 U.S.C. §114 does not protect Roth conversions but does protect the subsequent Roth distributions from any California tax after relocation.

Does the SECURE 2.0 §603 mandatory Roth catch-up interact differently for California residents?

§603 applies to California residents the same way it applies federally, because IRC §414 is inside the §17501 automatic-conformity perimeter. But because California has the highest state marginal rate in the country, the state-tax cost of §603 for high-earner California residents is larger than for participants in any other state. A §603-covered California participant loses up to 13.3% (12.3% + BHSA) of state tax deferral on the catch-up amount that would otherwise be pretax.

What is California's specified conformity date and which retirement provisions does it not conform to?

For most non-pension purposes, California conforms to the IRC as of January 1, 2015. Post-2015 federal changes do not apply for California unless the California Legislature passes a separate conformity statute. This affects SECURE Act, SECURE 2.0, and OBBBA provisions outside the §17501 automatic-conformity perimeter — including §529 plan rollovers to Roth IRAs, NIIT under §1411, and various §72(t) adjustments. Verify against the current FTB Summary of Federal Income Tax Changes report before assuming California follows.

Does California have an equivalent to the federal Net Investment Income Tax (NIIT)?

No. California does not impose a state-level NIIT equivalent. But California residents still pay the federal 3.8% NIIT under IRC §1411 on investment income above the $200,000 single or $250,000 MFJ MAGI threshold. Retirement account distributions are excluded from NIIT under §1411(c)(5); Roth conversions are also excluded at the conversion level, though the additional MAGI can spillover-trigger NIIT on other investment income in the conversion year.

Does the Pension Source Tax Act protect me from California tax after I relocate?

Yes, for §114-listed retirement income categories: §401(a) qualified plans, §403(a) and §403(b) annuities, §408 IRAs, §408A Roth IRAs, §457 governmental plans, §414(d) governmental plans, and NQDC paid as substantially equal periodic payments over life expectancy or at least 10 years. The shield is only as strong as the underlying domicile change — California can still challenge residency, and if it prevails the entire year is subject to California resident tax.

How does the Mental Health Services Tax (Behavioral Health Services Tax) affect high-income retirement contribution decisions?

R&TC §17043 imposes a 1% surtax on California taxable income above $1,000,000, applied at the same threshold for all filing statuses. Traditional §401(k) deferrals that reduce income from above to below the threshold save the full 13.3% marginal rate. Roth conversions that push income above the threshold pay the full 13.3% on the incremental amount. Time discretionary income events (conversions, RSU vesting, deferred comp payouts) to avoid unavoidable crossings within a single year.

What documentation should I keep to establish IRA and 401(k) basis for California purposes?

Same as federal — R&TC §17501 automatic conformity means California accepts the federal Form 8606 basis figure and federal plan recordkeeper statements without a separate California form. Add a residency file (California driver's license, voter registration, vehicle registration, homestead exemption filings, days-in-state records) if you are planning a large Roth conversion or a residency change — needed if California later challenges your residency status for the conversion year.

Methodology & Sources

This guide summarizes California's retirement-account tax framework as it applies to 2026 contributions and distributions. Federal limits are from IRS Notice 2025-67 (October 2025). California conformity analysis is based on R&TC §17501 automatic conformity to IRC §401 and Part I of Subchapter D of Chapter 1 of Subtitle A, and on the current Franchise Tax Board Publication 1005 (Pension and Annuity Guidelines) and Publication 1031 (Guidelines for Determining Resident Status). Community property analysis is based on the California Family Code as amended through 2026. This is not legal, tax, or investment advice. Consult a California-licensed CPA or tax attorney before executing any large one-year income event, relocation, or Roth conversion strategy.

  1. California Revenue and Taxation Code §17501 — automatic conformity to IRC §401 and Part I of Subchapter D of Chapter 1 of Subtitle A of the Internal Revenue Code. Codified at leginfo.legislature.ca.gov (California Legislative Information portal).
  2. California Revenue and Taxation Code §17024.5 — specified conformity date for the general California income tax provisions, currently January 1, 2015 for most non-pension purposes. Codified in the California Revenue and Taxation Code at leginfo.legislature.ca.gov.
  3. IRS Notice 2025-67 — 2026 cost-of-living adjustments applicable to dollar limitations for pension plans and other items. Published October 2025 at irs.gov/pub/irs-drop/n-25-67.pdf. Sets 2026 §401(k) elective deferral at $24,500, age-50 catch-up at $8,000, age-60-through-63 super catch-up at $11,250, §415(c) annual additions at $72,000, IRA base contribution at $7,500 with $1,100 age-50 catch-up.
  4. Franchise Tax Board Publication 1005 — Pension and Annuity Guidelines. Franchise Tax Board of the State of California, published annually at ftb.ca.gov/forms/misc/1005.html. Confirms California acceptance of federal Form 8606 basis figures and federal plan recordkeeper documentation for California return purposes.
  5. Franchise Tax Board — California Conformity to Federal Law. Franchise Tax Board of the State of California at ftb.ca.gov/tax-pros/law/conformity.html. States the current specified conformity date (January 1, 2015 for most non-pension provisions) and the automatic-conformity treatment under R&TC §17501 for pension provisions.
  6. Franchise Tax Board — Summary of Federal Income Tax Changes. Annual report analyzing federal legislative changes for California conformity purposes. Published at ftb.ca.gov/about-ftb/data-reports-plans/Summary-of-Federal-Income-Tax-Changes/. Definitive reference for whether California conforms to a specific SECURE Act, SECURE 2.0, or OBBBA provision.
  7. California Family Code §760 — Community Property. Codified at leginfo.legislature.ca.gov. Defines community property as property acquired by married persons during marriage while domiciled in California. Family Code §770 defines separate property; Family Code §751 provides equal management and control.
  8. Internal Revenue Code §408(g) — Community Property Laws. 26 U.S.C. §408(g). Provides that the taxation of an IRA "shall be determined without regard to any community property laws." Overrides state community property law for federal income tax purposes on IRA distributions and reporting.
  9. California Revenue and Taxation Code §17041 — Personal income tax rates. Codified at leginfo.legislature.ca.gov. Establishes the 9-bracket structure from 1% to 12.3% for California personal income tax. FTB publishes annual inflation-adjusted bracket thresholds in November of each year.
  10. California Revenue and Taxation Code §17043 — Additional tax on income over $1,000,000. Codified at leginfo.legislature.ca.gov. Original enactment as the Mental Health Services Tax under Proposition 63 (2004); renamed the Behavioral Health Services Tax by Proposition 1 approved by California voters in March 2024 (which reformed the spending mechanism but preserved the 1% surtax mechanic).
  11. FTB Publication 1005 — Pension and Annuity Guidelines, section on Roth Conversions. Confirms California treats Roth conversions as taxable events using the same computation as federal Form 8606. Available at ftb.ca.gov/forms/misc/1005.html.
  12. In re Bragg, State Board of Equalization (2003) — established the 15-factor residency analysis widely cited in California FTB residency audits. Summarized in FTB Legal Ruling 2020-01 and referenced in FTB Publication 1031 as the operative residency-analysis framework.
  13. Pension Source Tax Act of 1996, Public Law 104-95. Codified at 4 U.S.C. §114. Enacted January 10, 1996. Prohibits any state from imposing income tax on the retirement income of any individual who is not a resident or domiciliary of that state at the time the retirement income is paid. Enumerates the protected categories in §114(b)(1).
  14. California Revenue and Taxation Code §17014 — Resident defined. Codified at leginfo.legislature.ca.gov. Defines a resident as any individual who is in California for other than a temporary or transitory purpose, or who is domiciled in California but outside the state for a temporary or transitory purpose. Includes the 9-month presumption at §17014(a)(2).
  15. Franchise Tax Board Publication 1031 — Guidelines for Determining Resident Status. Available at ftb.ca.gov/forms/misc/1031.html. Provides the FTB's operational residency framework including the 15-factor Bragg analysis, the safe-harbor provisions for California-employer employees under R&TC §17014(d), and the domicile-vs-residency distinction.
  16. Internal Revenue Code §402A(c)(4)(E) — In-plan Roth rollovers from non-distributable amounts. Enacted by American Taxpayer Relief Act of 2012 §902. Provides the statutory basis for the mega backdoor Roth strategy through in-plan Roth rollovers of after-tax employee contributions. See also IRC §402A(c)(4)(D) (SECURE 2.0 §604 optional Roth employer contributions).
  17. Internal Revenue Code §414(v)(7) — Roth catch-up contributions for higher-earners. Enacted by SECURE 2.0 §603 (Consolidated Appropriations Act 2023, Public Law 117-328 Division T §603). Requires that age-50-and-over catch-up contributions by participants whose prior-year Social Security wages from the same-employer plan sponsor exceeded $150,000 (indexed) be made as designated Roth contributions.
  18. IRS Notice 2023-62 — Administrative transition relief for §603. Published August 2023. Provided the 2024-2025 two-year administrative transition relief that expired December 31, 2025, making 2026 the first-year-of-enforcement calendar year for §603. Available at irs.gov/pub/irs-drop/n-23-62.pdf.
This guide is educational content, not legal, tax, or investment advice. California retirement account taxation is fact-specific and depends on your residency status, filing status, community property circumstances, income level, and specific plan document terms. Consult a California-licensed CPA, tax attorney, or CFP before executing any Roth conversion, mega backdoor Roth strategy, or residency change strategy. The IRC provisions and California R&TC provisions cited in this guide are subject to legislative change; FTB conformity treatment is subject to annual FTB review and Legislative action. Verify current-year treatment against IRS Notice 2025-67 and the current FTB Summary of Federal Income Tax Changes report.