Weekmark

Calendar week · ISO 8601

Week 51, 2025

Monday 15 December – Sunday 21 December 2025

  1. Mon15Dec
  2. Tue16Dec
  3. Wed17Dec
  4. Thu18Dec
  5. Fri19Dec
  6. Sat20Dec
  7. Sun21Dec
ISO week
2025-W51
Copy as
CW51 (15–21 Dec)
Quarter
Q4 2025
Weeks in 2025
52
US week number
51

Week 51 is also written KW 51 (Kalenderwoche) or CW 51. ISO weeks start on Monday, and week 1 is the week with the year’s first Thursday. US calendars start weeks on Sunday and count the week with 1 January as week 1, so they give Monday 15 Dec to Saturday 20 Dec the same number: week 51.