Day of the Week Calculator
NewFind out what day of the week any date falls on, plus its day-of-year number, leap year status, and approximate week number.
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Extra details
Frequently Asked Questions
How far back or forward can I check a date?
The tool uses the browser's native Date object internally, which reliably handles dates across a very wide range (centuries in either direction) — though note it computes using the proleptic Gregorian calendar, which wasn't actually in use everywhere before the 1500s-1900s depending on the country.
Why does the tool use UTC internally instead of my local time zone?
Using UTC avoids a subtle bug where a date picker's midnight value could shift to the previous or next calendar day when interpreted in a browser's local time zone — the day of the week for a calendar date shouldn't depend on where you are.
What does "day of year" mean?
It's the sequential number of that date within its year — January 1st is day 1, and December 31st is day 365 (or 366 in a leap year).
Is the week number shown the same as the ISO 8601 week number?
No — this is a simplified approximation based on day-of-year and January 1st's weekday, useful for a rough sense of "which week of the year," but it doesn't follow the precise ISO 8601 rule (which defines week 1 as the week containing the year's first Thursday).