How to find the ISO week number in 3 easy steps
- 1
Pick the date
Any date you need a week number for.
- 2
Read the week
ISO week number and week-year appear instantly.
- 3
Check the extras
Quarter and day of year are listed too.
Why use the week number calculator tool from Super Utility Hub?
Sprint planning, payroll cycles, and project tracking all run on week numbers — and the ISO standard has its own quirks (week 1 can start in the previous year).
This calculator returns the ISO week number and week-year for any date, plus the quarter and day of year.
- Processes everything in your browser — no upload servers involved
- Free forever with unlimited uses
- Works on Windows, macOS, Linux, Android and iOS
- No watermark or branding on your output, ever
Frequently asked questions
What is an ISO week-year?
Some years have 53 weeks, and week 1 can begin in late December. The week-year may differ from the calendar year for early January dates.
What is today's week number?
The calculator accepts any date — today included — so it doubles as a current week number display.
How does ISO define week 1?
Week 1 is the week containing the first Thursday of the year, or equivalently the week with January 4th in it.