How many weeks are in 2025?
2025 has 52 weeks in ISO 8601, because it starts on a Wednesday. In the US system, where week 1 is the week of January 1 and partial weeks count, 2025 runs from week 1 to week 53. The last US week starts on Sunday, Dec 28, 2025.
ISO week 1 starts early, on Monday, Dec 30, 2024, because the week that holds January 1 also holds the first Thursday of 2025. At the other end, the days from Dec 29, 2025 on are already ISO week 1 of 2026.
US week 1 runs from Dec 29, 2024 to Jan 4, 2025. Because US weeks start on Sunday and ISO weeks on Monday, the same number never covers exactly the same days. For most of 2025, a date has the same number in both systems from Monday to Saturday, and the US number is one higher on Sundays.
Weeks month by month
January: US weeks 1 to 5; February: US weeks 5 to 9; March: US weeks 9 to 14; April: US weeks 14 to 18; May: US weeks 18 to 22; June: US weeks 23 to 27; July: US weeks 27 to 31; August: US weeks 31 to 36; September: US weeks 36 to 40; October: US weeks 40 to 44; November: US weeks 44 to 49; December: US weeks 49 to 53. In ISO numbering, January 2025 starts in week 1 and December ends in week 1 (of 2026).
2025 week numbers with dates
| Week | US (Sunday to Saturday) | ISO 8601 (Monday to Sunday) |
|---|---|---|
| 1 | Dec 29, 2024 to Jan 4 | Dec 30, 2024 to Jan 5 |
| 2 | Jan 5 to Jan 11 | Jan 6 to Jan 12 |
| 3 | Jan 12 to Jan 18 | Jan 13 to Jan 19 |
| 4 | Jan 19 to Jan 25 | Jan 20 to Jan 26 |
| 5 | Jan 26 to Feb 1 | Jan 27 to Feb 2 |
| 6 | Feb 2 to Feb 8 | Feb 3 to Feb 9 |
| 7 | Feb 9 to Feb 15 | Feb 10 to Feb 16 |
| 8 | Feb 16 to Feb 22 | Feb 17 to Feb 23 |
| 9 | Feb 23 to Mar 1 | Feb 24 to Mar 2 |
| 10 | Mar 2 to Mar 8 | Mar 3 to Mar 9 |
| 11 | Mar 9 to Mar 15 | Mar 10 to Mar 16 |
| 12 | Mar 16 to Mar 22 | Mar 17 to Mar 23 |
| 13 | Mar 23 to Mar 29 | Mar 24 to Mar 30 |
| 14 | Mar 30 to Apr 5 | Mar 31 to Apr 6 |
| 15 | Apr 6 to Apr 12 | Apr 7 to Apr 13 |
| 16 | Apr 13 to Apr 19 | Apr 14 to Apr 20 |
| 17 | Apr 20 to Apr 26 | Apr 21 to Apr 27 |
| 18 | Apr 27 to May 3 | Apr 28 to May 4 |
| 19 | May 4 to May 10 | May 5 to May 11 |
| 20 | May 11 to May 17 | May 12 to May 18 |
| 21 | May 18 to May 24 | May 19 to May 25 |
| 22 | May 25 to May 31 | May 26 to Jun 1 |
| 23 | Jun 1 to Jun 7 | Jun 2 to Jun 8 |
| 24 | Jun 8 to Jun 14 | Jun 9 to Jun 15 |
| 25 | Jun 15 to Jun 21 | Jun 16 to Jun 22 |
| 26 | Jun 22 to Jun 28 | Jun 23 to Jun 29 |
| 27 | Jun 29 to Jul 5 | Jun 30 to Jul 6 |
| 28 | Jul 6 to Jul 12 | Jul 7 to Jul 13 |
| 29 | Jul 13 to Jul 19 | Jul 14 to Jul 20 |
| 30 | Jul 20 to Jul 26 | Jul 21 to Jul 27 |
| 31 | Jul 27 to Aug 2 | Jul 28 to Aug 3 |
| 32 | Aug 3 to Aug 9 | Aug 4 to Aug 10 |
| 33 | Aug 10 to Aug 16 | Aug 11 to Aug 17 |
| 34 | Aug 17 to Aug 23 | Aug 18 to Aug 24 |
| 35 | Aug 24 to Aug 30 | Aug 25 to Aug 31 |
| 36 | Aug 31 to Sep 6 | Sep 1 to Sep 7 |
| 37 | Sep 7 to Sep 13 | Sep 8 to Sep 14 |
| 38 | Sep 14 to Sep 20 | Sep 15 to Sep 21 |
| 39 | Sep 21 to Sep 27 | Sep 22 to Sep 28 |
| 40 | Sep 28 to Oct 4 | Sep 29 to Oct 5 |
| 41 | Oct 5 to Oct 11 | Oct 6 to Oct 12 |
| 42 | Oct 12 to Oct 18 | Oct 13 to Oct 19 |
| 43 | Oct 19 to Oct 25 | Oct 20 to Oct 26 |
| 44 | Oct 26 to Nov 1 | Oct 27 to Nov 2 |
| 45 | Nov 2 to Nov 8 | Nov 3 to Nov 9 |
| 46 | Nov 9 to Nov 15 | Nov 10 to Nov 16 |
| 47 | Nov 16 to Nov 22 | Nov 17 to Nov 23 |
| 48 | Nov 23 to Nov 29 | Nov 24 to Nov 30 |
| 49 | Nov 30 to Dec 6 | Dec 1 to Dec 7 |
| 50 | Dec 7 to Dec 13 | Dec 8 to Dec 14 |
| 51 | Dec 14 to Dec 20 | Dec 15 to Dec 21 |
| 52 | Dec 21 to Dec 27 | Dec 22 to Dec 28 |
| 53 | Dec 28 to Jan 3, 2026 | No ISO week 53 |
Holidays by week number in 2025
Federal holidays and Easter, with their week in each system. 1 of these 12 dates have a different number in the two systems, so say which one you mean when you plan around them. None of the federal holidays falls on a weekend this year.
| Holiday | Date | US week | ISO week |
|---|---|---|---|
| New Year’s Day | Wed, Jan 1 | 1 | 1 |
| Martin Luther King Jr. Day | Mon, Jan 20 | 4 | 4 |
| Presidents’ Day | Mon, Feb 17 | 8 | 8 |
| Easter Sunday | Sun, Apr 20 | 17 | 16 |
| Memorial Day | Mon, May 26 | 22 | 22 |
| Juneteenth | Thu, Jun 19 | 25 | 25 |
| Independence Day | Fri, Jul 4 | 27 | 27 |
| Labor Day | Mon, Sep 1 | 36 | 36 |
| Columbus Day | Mon, Oct 13 | 42 | 42 |
| Veterans Day | Tue, Nov 11 | 46 | 46 |
| Thanksgiving | Thu, Nov 27 | 48 | 48 |
| Christmas Day | Thu, Dec 25 | 52 | 52 |
Writing a date as an ISO week date
ISO 8601 can also write a date as year, week and weekday. Thanksgiving 2025, Nov 27, 2025, becomes 2025-W48-4: week 48, day 4 (Thursday). Christmas Day becomes 2025-W52-4. Planning tools and some spreadsheets accept this form directly.
Other years: week numbers 2026. For any single date, the week number tool gives the week in one tap, and the day of the week calculator tells you which weekday it falls on.