Date
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How this calculator works
Enter a date to see its weekday, its position in the year and its ISO week number. Dates are read on the Gregorian calendar, including for years before the calendar was adopted (the proleptic Gregorian calendar), so historical dates recorded under the Julian calendar will not match.
Formula
- Weekday follows from the number of days since a known reference date, modulo 7
- Day of year = date − January 1 + 1
- Leap year: divisible by 4, except century years not divisible by 400
Worked example
July 4, 2026
- Date
- 2026-07-04
ResultSaturday
Saturday, July 4, 2026 is day 185 of 2026.
Frequently asked questions
What day of the week was I born?
Enter your date of birth. The headline shows the weekday.
Why does a historical date show a different weekday than my source?
Before 1582 (and later in many countries, such as 1752 in Britain and its colonies) the Julian calendar was in use. This tool applies Gregorian rules to every date.
How do I know if a year is a leap year?
A year is a leap year if it is divisible by 4, unless it is a century year not divisible by 400. So 2000 and 2024 are leap years; 1900 and 2100 are not.
Sources
More date & time calculators
Results are estimates based on the values you enter and the published method shown above. They do not replace professional medical, financial or legal advice. Method reviewed October 7, 2026. About this site