Week Number Calculator
Convert any date to an ISO or US-style week number, or find the date range for a week number.
Week 40 of 2026
ISO week for 2026-09-28 in UTC.
- Starts
- 2026-09-28
- Ends
- 2026-10-04
- Remaining
- 13 weeks
- Input date
- 2026-09-28
- Week system
- ISO
- Week number
- Week 40 of 2026
- Week starts
- 2026-09-28
- Week ends
- 2026-10-04
- Day of year
- 271
- Quarter
- Q3
- Weeks remaining
- 13
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Two-way week conversion
Use the date converter above, or enter a week number below to find the date range.