Free Tools for a Smarter YouWeek Number Calculator
See today's week number, find the week of any date in the ISO (Monday start) or US (Sunday start) system, and look up the dates of any week of a year.
- PrivateYour numbers never leave this device
- No uploadsProcessed in your browser, not on a server
- 100% freeNo signup, no watermark, no trial
- UnlimitedUse it as often as you like, no daily caps
Week number of a date
Pick a date.
Dates of a week number
How to use the Week Number
- Read this week's number at the top, or pick another date.
- To find the dates of a week, choose ISO or US and type the year and week number.
- Open “All weeks” for the whole year's list, and copy the answer if you need it.
Frequently asked questions
What week number is it today?
The top of the page shows it, worked out from your device's date. Most of the world, including business calendars in Europe and Asia, uses the ISO week.
What is the difference between ISO and US week numbers?
ISO weeks start on Monday and week 1 is the week with the year's first Thursday, so a week can belong to the previous or next year. US weeks (as in Excel's WEEKNUM) start on Sunday and week 1 is the week with 1 January.
Does a year have 52 or 53 weeks?
Most years have 52 ISO weeks; some, such as 2026, have 53. Counted the US way, a year has 53 weeks, and 54 in a leap year that starts on a Saturday (2028).
Which week does 1 January belong to?
In ISO it can be the last week of the year before: 1 January 2027 is in week 53 of 2026. In the US system it is always week 1.