Week 51 of 2025
December 15 – December 21, 2025
| Monday | December 15, 2025 | Mon · week starts |
| Tuesday | December 16, 2025 | |
| Wednesday | December 17, 2025 | |
| Thursday | December 18, 2025 | |
| Friday | December 19, 2025 | |
| Saturday | December 20, 2025 | |
| Sunday | December 21, 2025 | Sun · week ends |
All weeks of 2025
2025 is an ISO year with 52 weeks.
About ISO week 51 of 2025
ISO 8601 weeks start on Monday and end on Sunday. Week 51 of 2025 begins on Monday, December 15, 2025 and ends on Sunday, December 21, 2025. Week numbering follows the international standard: week 1 of a year is the week containing the first Thursday of January, which is why some calendar dates near January 1st belong to the previous or next ISO year.
The ISO week system is the standard for business reporting across Europe and much of the world. The US convention differs: weeks start on Sunday and week 1 contains January 1st, so US week numbers can be one ahead of or behind ISO numbers near year boundaries.
Frequently asked questions
What dates are in week 51 of 2025?
Week 51 of 2025 spans December 15 – December 21, 2025: Monday December 15 through Sunday December 21.
When is week 51 of 2025?
Week 51 of 2025 started 316 days ago, on Monday, December 15, 2025.
Why does 2025 have 52 weeks?
2025 has the usual 52 ISO weeks. Only years starting on a Thursday (or a Wednesday in a leap year) get a 53rd week.