Week Number Calculator
Find the current week number, or the week number for any date. ISO 8601 week numbering.
📐 How We Calculate This
Our calculators use industry-standard formulas sourced from authoritative references including government agencies, academic institutions, and professional organizations. We validate all calculations against multiple independent sources.
Results are estimates for educational purposes. Professional advice from a licensed expert is recommended for important financial, health, or legal decisions.
📚 Sources & References
Frequently Asked Questions
What is the ISO week number?
ISO 8601 defines week 1 as the week containing the first Thursday of the year. Weeks start on Monday. Most of the world uses this standard.
What week of the year is it right now?
Use this calculator with today's date to find the current week number. The year has 52 or 53 weeks.
Why do some years have 53 weeks?
A year has 53 ISO weeks when January 1 is a Thursday (or Wednesday/Thursday in a leap year). This happens roughly every 5-6 years.