ISO week calendar
Week 51 2026
ISO week 51 of 2026 runs from Monday, December 14, 2026 to Sunday, December 20, 2026.
Date Time Encyclopedia answer, with calculation details and assumptions below.
ISO weeks start on Monday and end on Sunday. Week 1 is the week containing the first Thursday of the ISO week-numbering year.
Snapshot
Week 51 2026
ISO week 51 of 2026 runs from Monday, December 14, 2026 to Sunday, December 20, 2026.
ISO weeks start on Monday and end on Sunday. Week 1 is the week containing the first Thursday of the ISO week-numbering year.
- Week starts
- Monday, December 14, 2026
- Week ends
- Sunday, December 20, 2026
- ISO year
- 2026
- Weeks in ISO year
- 53
ISO week 51, 2026
- MonDec 14, 2026Week start
- TueDec 15, 20262026-W51
- WedDec 16, 20262026-W51
- ThuDec 17, 20262026-W51
- FriDec 18, 20262026-W51
- SatDec 19, 20262026-W51
- SunDec 20, 2026Week end
Method
Find the Monday of ISO week 1, then add seven days for each week after it.
ISO week context
Week 51 2026 uses the ISO week-date system: weeks start Monday, end Sunday, and week 1 is tied to the first Thursday of the ISO year.
Compare nearby ISO weeks
Adjacent week pages help verify handoffs between reporting periods, sprints, payroll periods, and weekly plans.
Related Lookups
FAQ
When does this ISO week start?
Week 51 of 2026 starts on Monday, December 14, 2026.
When does this ISO week end?
Week 51 of 2026 ends on Sunday, December 20, 2026.