Weekmark

Calendar week · ISO 8601

Week 40, 2025

Monday 29 September – Sunday 5 October 2025

  1. Mon29Sep
  2. Tue30Sep
  3. Wed1Oct
  4. Thu2Oct
  5. Fri3Oct
  6. Sat4Oct
  7. Sun5Oct
ISO week
2025-W40
Copy as
CW40 (29 Sep – 5 Oct)
Quarter
Q4 2025
Weeks in 2025
52
US week number
40

Week 40 is also written KW 40 (Kalenderwoche) or CW 40. 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 29 Sep to Saturday 4 Oct the same number: week 40.