Week Number Calculator
Date
ISO week number identifies which week of the year a date falls in. ISO 8601 defines week 1 as containing the first Thursday of the year, with weeks starting on Monday. Week numbers run from 1 to 52 or 53.
- 1Week 1 contains the first Thursday of the year
- 2Weeks always start on Monday
- 3Year can have 52 or 53 weeks
- 4Days in late December may belong to week 1 of the next year
1 January 2024=Monday; Week 1 of 2024 (2024 starts on a Monday — rare!)
| Fact | Detail |
|---|---|
| Week starts | Monday (ISO 8601) |
| Week 1 | Contains first Thursday of year |
| Total weeks | 52 (most years) or 53 |
| Max week 53 | Occurs in long years |
| Jan 1 can be | Week 1 or week 52/53 of prior year |
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