Week number: what week is it?
…
How to use this calculator?
1. The current week number is shown as soon as the page opens
2. Pick a date to get its week number and its Monday to Sunday dates
3. Browse the list of every week of the year, and change year with the arrows
4. Share the link to send the week shown
Quick answer
How do you find the week number of a date?
Find the Thursday of your date's week, then count how many Thursdays there have been since the start of the year: that is the ISO week number. For example, Saturday 31 October 2026 is in the week of Thursday 29 October, the 44th Thursday of 2026, so it is week 44 (Monday 26 October to Sunday 1 November).
| Date | ISO week |
|---|---|
| Thursday 1 January 2026 | Week 1 of 2026 |
| Saturday 31 October 2026 | Week 44 of 2026 |
| Monday 28 December 2026 | Week 53 of 2026 |
| Friday 1 January 2027 | Week 53 of 2026 |
| Monday 4 January 2027 | Week 1 of 2027 |
About the Week Number
What is it?
This tool gives the current week number according to ISO 8601, the standard used across Europe. It also shows the week of any date, with its Monday to Sunday dates, and the full list of the year's weeks.
Why use it?
Week numbers are used everywhere at work: schedules, delivery dates, holidays, payroll, production planning or school terms. Saying "delivery in week 12" is shorter than a date, as long as you know which days it covers.
How does it work?
Under ISO 8601, a week starts on Monday and week 1 is the week that contains the first Thursday of January (which is also the week containing 4 January). A year therefore has 52 or 53 weeks. The first days of January can belong to the last week of the previous year, and the last days of December to week 1 of the next year.
Usage tips
- 1 January 2027 is a Friday, so it belongs to week 53 of 2026
- A year has 53 weeks when it starts on a Thursday, or on a Wednesday in a leap year
- In the United States weeks start on Sunday and are counted differently: say "ISO week" with international partners
- In Excel or Google Sheets, the ISOWEEKNUM function gives the same result
- Share the link to send a specific week to your colleagues