Backdoor Roth IRA Calculator (2026)

What this calculator models

The backdoor Roth IRA is a two-step maneuver for filers whose income exceeds the direct Roth IRA MAGI phaseout ceiling — $168,000 single or $252,000 joint for 2026 per IRS Notice 2025-67. Step 1: contribute up to $7,500 ($8,600 if age 50+) to a Traditional IRA and elect nondeductible treatment. Step 2: convert the Traditional balance to a Roth IRA. Both steps are reported on IRS Form 8606 for the year of the conversion.

The trap that most calculators ignore is the pro-rata rule under IRC §408(d)(2). If you carry any pretax balance in any Traditional, SEP, or SIMPLE IRA — including a rollover IRA from a former employer's 401(k) — the pro-rata rule forces the conversion to be treated as a mix of basis and pretax dollars, and only the basis fraction escapes tax. This calculator makes the ratio explicit, computes the taxable portion, and quantifies the federal + state tax cost.

The 2026 IRA limits and Roth MAGI phaseouts

• IRA contribution limit: $7,500 base + $1,100 age-50 catch-up = $8,600 ceiling for 2026 (IRS Notice 2025-67).
• Roth IRA MAGI phaseout — single: $153,000 to $168,000. Above $168,000, no direct Roth contribution is permitted; backdoor route is the only path.
• Roth IRA MAGI phaseout — MFJ: $242,000 to $252,000. Above $252,000, direct Roth is closed.
• No income limit on the nondeductible Traditional contribution itself or on the Roth conversion. The backdoor route exists precisely because Congress capped direct Roth eligibility but never capped conversions (since the Tax Increase Prevention and Reconciliation Act of 2005 removed the conversion income limit effective 2010).

How to read the Form 8606 lines the calculator produces

• Line 1 — this year's nondeductible contribution.
• Line 2 — prior-year basis (running total of all after-tax dollars ever contributed).
• Line 3 — Line 1 + Line 2. Total basis so far.
• Line 5 — basis available for pro-rata (Line 3 minus any 2027 contributions attributed to 2026, usually zero).
• Line 6 — December 31 aggregate value of every Traditional, SEP, and SIMPLE IRA in your name. THE load-bearing number.
• Line 8 — amount converted to a Roth IRA during the year.
• Line 9 — Line 6 + Line 7 + Line 8. The denominator of the pro-rata ratio (total pie).
• Line 10 — Line 5 ÷ Line 9, capped at 1.000, rounded to 6 decimals. The basis ratio.
• Line 11 — Line 8 × Line 10. Tax-free portion of the conversion.
• Line 14 — Line 3 − Line 13. Basis carryforward to next year's Form 8606.
• Line 18 (Part II) — Line 8 − Line 11. Taxable portion of the conversion. Flows to Form 1040 Line 4b.

The reverse-rollover fix (IRC §408(d)(3)(A)(ii))

If you carry a large pretax rollover IRA and want a clean backdoor, the mechanical solution is to move that balance out of your name and into a workplace 401(k) that accepts incoming rollovers. The tax code explicitly permits this direction of movement, and the transferred amount is not counted on Form 8606 Line 6. Complete the rollover by December 31 of the tax year in which you want the pro-rata ratio to be 1.0, then execute the backdoor conversion any time after — even the same day.

About 91% of large-employer 401(k) plans accept incoming rollovers; roughly 70% of small-employer plans do. Check your plan's Summary Plan Description or ask HR. Toggle "Yes" on the reverse-rollover fix above to see side-by-side what the clean scenario would save you.

Related tools and reading

• Backdoor Roth IRA in 2026: the pro-rata trap, mega backdoor variant, and every mistake to avoid — the full guide this calculator serves.
• How to file Form 8606 in 2026: nondeductible IRAs, backdoor Roth, and the pro-rata rule line by line — paperwork walkthrough.
• Roth 401(k) vs Traditional 401(k) in 2026 — workplace-plan Roth-vs-Trad decision.
• SEP-IRA vs Solo 401(k) for freelancers in 2026 — the §408(d)(2) pro-rata trap makes SEP-IRA a worse backdoor target than Solo 401(k).
• Roth IRA Conversion Calculator — year-by-year projection of a larger conversion.
• Mega Backdoor Roth Calculator — the §415(c) $72,000 after-tax 401(k) variant.
• 401(k) Calculator — includes the SECURE 2.0 §603 mandatory Roth catch-up model.
• Roth IRA Calculator — direct Roth projection when MAGI is under phaseout.
• SEP IRA Calculator and SIMPLE IRA Calculator — self-employed / small-employer plan siblings.
• Retirement Calculator — combined-account projection.