Dates & time
ISO week date to calendar date
Turn a week-year, ISO week and weekday into a Gregorian calendar date.
A clear answer. Here’s how.
ISO weeks start Monday, and week 1 contains January 4 (the first Thursday). Week-year can differ from calendar year near New Year. Locates the requested date and verifies the resulting week-year/week to reject nonexistent week 53. Results must remain in years 0001–9999.
See a worked example
Worked example
A fixed demonstration, separate from the values you enter above.
- ISO week-year
- 2026
- ISO week number
- 42
- ISO weekday (Monday=1 … Sunday=7)
- 5
Example result
- Calendar date
- 2026-10-16
- Weekday
- Friday
- ISO week date
- 2026-W42-5