Date
Day of the Week Calculator
Weekday, ISO week number, day of the year, and days remaining for any date.
Inputs
Day of the Week Calculator
Result
Weekday
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How it's calculated
Zeller-style weekday; ISO 8601 week: week containing the Thursday of that day's week
Common questions
What is an ISO week number?
ISO 8601 numbers weeks so that week 1 contains the year's first Thursday. Weeks always start on Monday, and a year has 52 or 53 ISO weeks.
Is January 1 always day 1?
Yes. Day of year counts from January 1 = 1 through December 31 = 365 (or 366 in leap years).
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