6 min read
2026-02-12
A week number is the ordinal number of a week in the year (from 1 to 52 or 53). It's a convenient way to refer to a specific period: "meeting on week 15" is clearer than "sometime in mid-April."
The international standard ISO 8601 defines week numbering rules:
Weeks start on Monday
The first week of the year is the one containing the first Thursday of January
A year can have 52 or 53 weeks
| Date | Week Number |
|---|---|
| January 1, 2026 | Week 1 |
| February 15, 2026 | Week 7 |
| July 1, 2026 | Week 27 |
| December 31, 2026 | Week 53 or 1 |
Enter a date in our tool
Get the ISO standard week number
See which dates fall within that week
Days at the end of December can belong to week 1 of the following year, and days at the beginning of January can belong to week 52 or 53 of the previous year.
Determine the week number with the Week Number tool.
See also: Calendar, Date Difference, Age Calculator