ISO Week Numbers 2025
Find ISO week numbers and Monday-to-Sunday date ranges for 2025. The current week is calculated using the UTC calendar date; each ISO year contains 52 or 53 complete weeks.
Week 43, 2026
· UTC · 52 ISO weeks in 2025
Week dates in 2025
| ISO week | Monday | Sunday |
|---|---|---|
| 2025-W01 | ||
| 2025-W02 | ||
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| 2025-W48 | ||
| 2025-W49 | ||
| 2025-W50 | ||
| 2025-W51 | ||
| 2025-W52 |
Frequently asked questions
Which day starts the week?
Each calendar row starts on Monday and ends on Sunday, following ISO 8601.
How are ISO week numbers assigned?
Week 1 contains January 4, or equivalently the first Thursday of the year. Dates at either end of a year can belong to the adjacent ISO week-year.
Why do some years have 53 weeks?
An ISO year has 53 weeks when January 1 is a Thursday, or when a leap year starts on Wednesday.