Week Number
ISO week and locale week of year.
Loading tool
Pick a date and read the ISO week, weekday, and week-year. Monday is the ISO start. A US-style Sunday start is optional.
How to use this tool
- Set the dates or duration. Pick the clocks, dates, or timer length you need.
- Start or calculate. Run the timer or read the difference. Time zones use this browser.
- Copy the result. Copy timestamps or calendar values into your notes.
Week-year
Early January can belong to the previous ISO week-year. Late December can belong to the next. That is expected.
Frequently asked
Is week 53 real?
Some ISO years have 53 weeks. The page will say so.
Can I list every week in a year?
Yes. Export a table of start dates.
Does ISO week match my payroll week?
Only if payroll uses ISO. Many do not.
What weekday is day 1?
ISO: Monday. Locale mode follows the toggle.
Is the date uploaded?
No.