ISO Week Number
Find the ISO-8601 week number (1-53) for any date. Pick a date and instantly see which week of the year it falls in. Free and private, right in your browser.
Type or pick any date and instantly get its ISO 8601 week number (1-53), the week's Monday-to-Sunday date range, and its ISO week-year, handy for filling in timesheets, sprint planning, invoices, or any system that tracks work by week instead of by calendar date.
How to use it
- Enter a date, or leave it on today's date
- Read off the ISO week number and week-year
- Check the Monday-Sunday date range shown for that week
Frequently asked questions
- What's the difference between ISO week number and a regular calendar week?
- ISO 8601 weeks start on Monday, and Week 1 is the week containing the year's first Thursday (equivalently, the week with January 4th in it). This means late-December dates can fall in Week 1 of the next year, and early-January dates can fall in the last week (52 or 53) of the previous year.
- Can a year have 53 weeks?
- Yes. A year has 53 ISO weeks if January 1st falls on a Thursday, or if it's a leap year and January 1st falls on a Wednesday. Otherwise it has 52.
- Why does the tool show a different year than my date's calendar year?
- That's the ISO week-year, which can differ from the calendar year at the very start or end of December/January. For example, December 31, 2029 falls in ISO week 1 of 2030.
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Works offline
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