Day of the Week Calculator (Any Date)
Find what day of the week any date falls on — past, present, or future.
What this calculates
What day was your birthday in 1985? What day will Christmas fall on in 2050? This calculator returns the weekday for any date using the proleptic Gregorian calendar (extending current rules backward).
Formula & how it works
JavaScript Date.getDay() returns 0 (Sunday) through 6 (Saturday). Locale formatting provides the named weekday.
Worked example
July 20, 1969 (moon landing) → Sunday. December 25, 2050 → Sunday.
Frequently asked questions
Old-style dates?
Pre-1582 (or pre-1752 in the British Empire), the Julian calendar was used. This calculator uses Gregorian throughout — historical dates may differ by 10-13 days.
Future limits?
Reliable through year 275000. After that, JavaScript dates lose precision.
Leap years?
Handled automatically. Gregorian leap rule: divisible by 4, except centuries unless divisible by 400 (e.g., 2000 was leap, 1900 wasn't).
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