This is ISO week 39 of 2026
Today, Wednesday, September 23, 2026, sits in ISO week 39, which runs from Monday September 21, 2026 to Sunday September 27, 2026. 2026 has 53 ISO weeks in total, so 14 weeks remain after this one.
What week of the year is it?
Week 39. ISO 8601 numbers weeks from Monday to Sunday and puts week 1 wherever the first Thursday of January lands, which is the same as saying the week that holds at least four days of the new year. That rule is what makes week numbers portable between systems, and it is also why a January date can carry a week number in the fifties belonging to the previous year.
Week count by year
| Year | 1 January | ISO weeks | Week 1 starts |
|---|---|---|---|
| 2024 | Monday | 52 | January 1, 2024 |
| 2025 | Wednesday | 52 | December 30, 2024 |
| 2026 | Thursday | 53 | December 29, 2025 |
| 2027 | Friday | 52 | January 4, 2027 |
| 2028 | Saturday | 52 | January 3, 2028 |
| 2029 | Monday | 52 | January 1, 2029 |
| 2030 | Tuesday | 52 | December 31, 2029 |
A year carries a 53rd week only when 1 January is a Thursday, or when it is a leap year starting on a Wednesday. Across a full 400-year Gregorian cycle that happens in 71 years, which is why long years arrive at uneven gaps of five, six or eleven years rather than on a fixed rhythm.
Every ISO week
Questions
- What week of the year is it?
- ISO week 39 of 2026, running September 21, 2026 to September 27, 2026.
- How many weeks are in 2026?
- 53. See the 2026 week count.
- Which day starts an ISO week?
- Monday. A Sunday-first week is a different convention and can number the same date differently.
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