Week Number Calculator
Get ISO week numbers for any date — plan sprints and fiscal weeks correctly. Know Week 32 means late July instantly — free, local, no signup.
How to Use the Week Number Calculator
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Frequently Asked Questions
ISO week rules?
Weeks start Monday; week 1 contains the first Thursday (Jan 4 always in week 1). US Sunday-start systems differ — confirm which standard applies.
Week 53 years?
Most years have 52 ISO weeks; years starting Thursday (or leap years starting Wednesday) get 53. The tool reports correctly either way.
Sprint planning?
Name sprints by ISO week (2026-W32) for unambiguous cross-timezone references. Backlogs sort chronologically for free.
Do week counts upload?
No — math runs locally in your browser. Nothing leaves your device.
Which weeks do Jan 1 and Dec 31, 2026 fall in?
Jan 1 2026 (a Thursday) gives Week 1; Dec 31 2026 gives Week 53. The tool counts the Jan 1–3 partial week as week 1 (week = ceil((dayOfYear + Jan-1 weekday) / 7)), so year-end spills to 53 — this is not the ISO-8601 rule, so cross-check for compliance use.
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Last updated October 2026