Day of the Week Calculator
Find Day of Week
Formula
Uses the Gregorian calendar. ISO week = weeks since first Thursday of the year.
Frequently Asked Questions
How do you calculate the day of the week?
This calculator uses the JavaScript Date object which implements the Gregorian calendar. Historically, algorithms like Zeller's congruence or the Doomsday algorithm can calculate the day of the week from any date.
What is the ISO week number?
ISO 8601 defines week 1 as the week containing the first Thursday of the year. Weeks start on Monday. The last days of December may belong to week 1 of the next year.
What day of the week was January 1, 2000?
January 1, 2000 was a Saturday.
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