Week 51 2025: December 15–21, 2025
Week 51 starts on Monday, December 15, 2025 and ends on Sunday, December 21, 2025.
Quick answer
Week 51 of 2025 is the seven-day ISO week from December 15, 2025 to December 21, 2025. ISO weeks always run from Monday to Sunday.
Use week 51 in professional planning
This permanent week reference can be used in project plans, payroll notes, weekly reports, production schedules and deadline documents. Share the week number together with the ISO year and exact date range to avoid ambiguity around New Year.
For calculations that span more than one week, use the weeks between dates calculator. For work schedules, compare the same range with the business days calculator or open the project timeline calculator.
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FAQ
What are the dates for week 51 of 2025?
The dates are December 15, 2025 through December 21, 2025.
What day does this week start?
It starts on Monday.
What day does this week end?
It ends on Sunday.
How should I write this week in a report?
Use “ISO week 51 of 2025 (Dec 15–Dec 21, 2025)” so the week-year and date range are both clear.