Day of the Week Calculator
Choose any date, past or future, to see the weekday, the ISO week number and the day of the year.
Your details
Result
Fill in the fields to see your result.
Good to know: 1 January 2000 was a Saturday.
About this tool
Find the weekday for any date, past or future, along with the day of the year, ISO week number and days remaining in the year.
Formula
Uses the fixed 400-year Gregorian weekday cycle. ISO week: week 1 contains the first Thursday of January; weeks start Monday.
Reference values
- ISO-8601 weeks: 1–53, starting Monday
- Ordinal date: 1 = 1 January
- Leap years add a day to February
Questions people ask
How do I find the day of the week for a date?
Pick the month, day and year and the weekday appears.
What is an ISO week number?
Weeks start on Monday, and week 1 is the week containing the first Thursday of January.
Does it work for dates before 1900?
It uses the Gregorian calendar, which was adopted at different times in different countries.
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How we calculate this
We use the standard published formula or definition for this calculation, and we show the working so you can check it.
Spotted a mistake? Tell us and we'll check it. How we check our calculators