Week Calculator
Discover which week of the year a date falls into, along with the exact start and end dates for both Sunday-start and Monday-start weeks.
Date: Tuesday, November 25, 2025
ISO week
Week 48, 2025
Gregory week (Sunday start)
Sunday, November 23, 2025 → Saturday, November 29, 2025
ISO week (Monday start)
Monday, November 24, 2025 → Sunday, November 30, 2025
How to Use This Calculator
Choose a date
Use the picker to select any day in the year.
Review ISO week details
See the ISO week number and year—helpful for global schedules.
Compare start/end dates
View both Monday-based and Sunday-based week boundaries for planning purposes.
Formula
ISO Week: shift date to Thursday → compute week number from Jan 4
Monday Start = Date + (1 − Weekday) (with Sunday treated as 7)
Sunday Start = Date − Weekday
Example: 2025-11-09 → ISO Week 45 • Monday-start week = 2025-11-03 → 2025-11-09 • Sunday-start week = 2025-11-09 → 2025-11-15.
Why Week Numbers Matter
- Align global project timelines with ISO week numbers.
- Coordinate sprint planning or release cycles in agile workflows.
- Convert calendar holidays into week-based schedules.
- Track weekly goals and metrics without date confusion.
Frequently Asked Questions
Why does the ISO week sometimes belong to the previous/next year?
ISO week numbering ensures week 1 contains the first Thursday. Dates near year boundaries may fall into adjacent week years.
Do these weeks respect daylight saving time?
Yes—week boundaries are based on local calendar days, independent of DST shifts.
Can I use Saturday as the start of the week?
This tool supports Sunday or Monday. For custom start days, adapt the formula by shifting weekdays accordingly.
How can I export week data?
Copy the start/end dates into spreadsheets or calendars to build weekly schedules or reports.