Week number calculator (ISO week)
Pick a date to see its ISO week number and its week of the month. Weeks start on Monday.
ISO week
Week of the month
| Week | Monday | Sunday |
|---|
How to use
- Pick a date; it starts as today.
- The ISO week, the week of the month and the week's Monday to Sunday appear.
- The table lists every week of that year.
Questions
How are ISO weeks numbered?
Under ISO 8601 weeks start on Monday, and week 1 is the week with the year's first Thursday. So 1 January can fall in week 52 or 53 of the previous year, and late December in week 1 of the next.
Can a year have 53 weeks?
Yes: years starting on a Thursday (or a Wednesday, in leap years), such as 2026.
How is the week of the month counted?
A Monday-to-Sunday week belongs to the month of its Thursday. Some calendars count differently (Sunday start, or the week containing the 1st as week 1).
Is it the same as US week numbers?
Not always. A common US scheme starts weeks on Sunday with the week containing 1 January as week 1, which can differ from ISO by one.
Is anything saved?
No. It is calculated in your browser.
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