Each row shows the ISO week number, the Monday it starts on, and the Sunday it ends on.
Week numbers 2025 — all 52 weeks
| Week | Start (Monday) | End (Sunday) |
|---|---|---|
| W01 | 30 Dec 2024 | 5 Jan 2025 |
| W02 | 6 Jan | 12 Jan |
| W03 | 13 Jan | 19 Jan |
| W04 | 20 Jan | 26 Jan |
| W05 | 27 Jan | 2 Feb |
| W06 | 3 Feb | 9 Feb |
| W07 | 10 Feb | 16 Feb |
| W08 | 17 Feb | 23 Feb |
| W09 | 24 Feb | 2 Mar |
| W10 | 3 Mar | 9 Mar |
| W11 | 10 Mar | 16 Mar |
| W12 | 17 Mar | 23 Mar |
| W13 | 24 Mar | 30 Mar |
| W14 | 31 Mar | 6 Apr |
| W15 | 7 Apr | 13 Apr |
| W16 | 14 Apr | 20 Apr |
| W17 | 21 Apr | 27 Apr |
| W18 | 28 Apr | 4 May |
| W19 | 5 May | 11 May |
| W20 | 12 May | 18 May |
| W21 | 19 May | 25 May |
| W22 | 26 May | 1 Jun |
| W23 | 2 Jun | 8 Jun |
| W24 | 9 Jun | 15 Jun |
| W25 | 16 Jun | 22 Jun |
| W26 | 23 Jun | 29 Jun |
| W27 | 30 Jun | 6 Jul |
| W28 | 7 Jul | 13 Jul |
| W29 | 14 Jul | 20 Jul |
| W30 | 21 Jul | 27 Jul |
| W31 | 28 Jul | 3 Aug |
| W32 | 4 Aug | 10 Aug |
| W33 | 11 Aug | 17 Aug |
| W34 | 18 Aug | 24 Aug |
| W35 | 25 Aug | 31 Aug |
| W36 | 1 Sep | 7 Sep |
| W37 | 8 Sep | 14 Sep |
| W38 | 15 Sep | 21 Sep |
| W39 | 22 Sep | 28 Sep |
| W40 | 29 Sep | 5 Oct |
| W41 | 6 Oct | 12 Oct |
| W42 | 13 Oct | 19 Oct |
| W43 | 20 Oct | 26 Oct |
| W44 | 27 Oct | 2 Nov |
| W45 | 3 Nov | 9 Nov |
| W46 | 10 Nov | 16 Nov |
| W47 | 17 Nov | 23 Nov |
| W48 | 24 Nov | 30 Nov |
| W49 | 1 Dec | 7 Dec |
| W50 | 8 Dec | 14 Dec |
| W51 | 15 Dec | 21 Dec |
| W52 | 22 Dec | 28 Dec |
Key dates in 2025 by week number
Useful reference for planning: which ISO week do major fixed dates fall in?
| Date | Day | ISO Week |
|---|---|---|
| January 1, 2025 | Wednesday | W01 |
| February 14, 2025 | Friday | W07 |
| March 20, 2025 (spring equinox) | Thursday | W12 |
| June 21, 2025 (summer solstice) | Saturday | W25 |
| September 22, 2025 (autumn equinox) | Monday | W39 |
| October 31, 2025 | Friday | W44 |
| December 21, 2025 (winter solstice) | Sunday | W51 |
| December 25, 2025 | Thursday | W52 |
| December 31, 2025 | Wednesday | W01 of 2026 |
FAQ
What week number is January 1, 2025?
January 1, 2025 falls in ISO week 1 of 2025. Week 1 started on Monday, December 30, 2024.
What week number is Christmas 2025?
December 25, 2025 (Thursday) is in ISO week 52 of 2025.
What week number is December 31, 2025?
December 31, 2025 (Wednesday) is in ISO week 1 of 2026 — the last days of December 2025 belong to the first week of 2026.
How many weeks does 2025 have?
2025 has 52 ISO weeks. The last week of 2025 (W52) ends on Sunday, December 28, 2025.