Day of the Week Calculator — Weekday, Ordinal Day, and ISO Week
Find the weekday, day of year, and ISO week for a valid Gregorian calendar date.
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How to use it
Pick a date to see which day of the week it falls on.
Good to know
Uses the proleptic Gregorian calendar for all dates.
Check a date on a calendar
Enter a complete date in YYYY-MM-DD form. The date 2026-09-27 returns Sunday, September 27, 2026, day 270 of the year, and ISO week 39. This is handy for planning an event or checking an archived date.
Historical records can use another calendar
The calculator uses the proleptic Gregorian calendar and UTC dates for every valid input. A historic record from before a place adopted the Gregorian calendar can have a different contemporary weekday or date convention. It also cannot account for a local time-zone boundary; use a local calendar service when an event’s precise civil date matters.
Frequently asked questions
What day of the week was I born?
Enter your date of birth to see the weekday.
Does it work for future dates?
Yes. Enter any date to find the weekday, day of the year, and ISO week number.
Which calendar is used?
The Gregorian calendar. Historic dates before a country adopted it may differ from records of the time.