Iso Week To Date Calculator
Convert an ISO week-year, week number and weekday into a calendar date.
Result for the values shown.
Calculations run in your browser.
What to enter
| Input | Meaning and units |
|---|---|
| Week year | integer 1..9999 |
| Week | integer 1..53 |
| Weekday | integer 1..7 |
Understanding your result
Calendar results use the stated counting and anniversary convention. Complete months and years differ from fixed day counts.
Common mistakes
- Counting both end dates when the method excludes a boundary, or assuming all months have equal length.
- Assuming the ISO week-year always equals the calendar year.
Check your calculation
- Test a short known interval and a leap-day boundary; for working days, verify your holiday list.
Calculation checks, sources and review limits
What calendar date corresponds to an ISO week and weekday?
Convert an ISO week-year, week number and weekday into a calendar date.
Common uses
- Convert an ISO week-year, week number and weekday into a calendar date.
How it works
Find Monday of ISO week1 from Jan4; add 7*(week-1)+(weekday-1); validate roundtrip. Calendar arithmetic uses the proleptic Gregorian calendar. Explicit calendar dates are independent of local daylight-saving changes. Month/year additions clamp to the last valid day of the destination month. Timestamp arithmetic requires a stated UTC offset and excludes leap seconds.
Worked example
Enter Week year: 2020; Week: 53; Weekday: 5. The result is Date: 2021-01-01.
FAQ
What calendar date corresponds to an ISO week and weekday?
Find Monday of ISO week1 from Jan4; add 7*(week-1)+(weekday-1); validate roundtrip. Calendar arithmetic uses the proleptic Gregorian calendar. Explicit calendar dates are independent of local daylight-saving changes. Month/year additions clamp to the last valid day of the destination month. Timestamp arithmetic requires a stated UTC offset and excludes leap seconds.
What assumptions and limits apply?
Reject week53 if ISO week-year has only 52 weeks.