Time
Day of the Week Calculator
Find the weekday for any valid calendar date.
Day of the Week Calculator result
- Full date
- Thursday, September 17, 2026
- ISO weekday
- 4 (Monday = 1)
- ISO week / week-year
- 2026-W38
- Week range
- 2026-09-14 through 2026-09-20
- Day of year
- 260
- Days remaining in year
- 105
- Calendar quarter
- Q3
- Day type
- Weekday
- Position in month
- 3rd Thursday of September
Weekday uses the proleptic Gregorian calendar. ISO weeks begin Monday and can belong to an adjacent week-year.
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How this tool works
The valid Gregorian date is evaluated at UTC. ISO weekday uses Monday = 1; ISO week 1 contains the year’s first Thursday; week boundaries run Monday through Sunday.
Assumptions
The entered ISO calendar date is interpreted in the proleptic Gregorian calendar at UTC. ISO weekday, week-year boundaries, day-of-year, quarter, and the date’s position within its month are derived from that same date.
Limits to know
The result uses the proleptic Gregorian calendar and ISO 8601 week rules. Historical locations adopted Gregorian dates at different times, so very old civil records may use another calendar.