Day of the Week Calculator

It builds the date at midnight UTC and reads the weekday index the calendar assigns to it, then maps that to a name from Sunday to Saturday. This is pure date arithmetic, so there is no lookup table to go stale and no rounding.

No. The date is anchored to UTC before the weekday is read, so January 1, 2000 is Saturday whether you are in Tokyo or Los Angeles. A calendar date has one weekday, and the tool reports it consistently for everyone.

Yes. It uses the proleptic Gregorian calendar, which extends today's calendar rules backward and forward without limit, so a date in the 1700s and a date in 2200 both return a correct, consistent weekday.

The math is exact, but be aware that the Gregorian calendar was only adopted from 1582 onward, and different countries switched at different times. For dates before then, the tool gives the proleptic Gregorian weekday, which may differ from the Julian calendar date recorded in historical documents.

Leap years are built into the calendar rules, so February 29 is accepted only in real leap years. February 29, 2024 returns Thursday, while February 29, 1900 is rejected because 1900 was not a leap year under the Gregorian century rule.

Saturday and Sunday are treated as the weekend, and Monday through Friday as weekdays. This follows the common Western convention. If your region treats other days as the weekend, use the weekday name and apply your own rule.

The field uses a standard date picker and expects the ISO form YYYY-MM-DD, for example 2026-06-10. The input must be a real calendar date, so impossible values like February 30 or a month of 13 are rejected with an error.

The field starts on your current local date as a convenient starting point, so you can immediately see today's weekday. Change it to any other date to look that one up instead.

Yes. The whole calculation runs in your browser using date arithmetic. Nothing you enter is uploaded, logged or stored anywhere.