Relative to today
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Day of Week Calculator
Enter any date — past, present, or future — and we tell you what day it was. Jan 1, 2000 was a Saturday — check it.
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How we know
We use JavaScript's native Date object, which tracks days since January 1, 1970 UTC internally, then call getDay() (0 = Sunday through 6 = Saturday). This works for dates from roughly April 200 million BCE to 275,760 CE — everything you will ever need.
Fun day-of-week facts
The 13th falls on a Friday more often than any other weekday on average — 688 times per 400-year Gregorian cycle vs 684 for each other day. Jan 1, 2000 = Saturday. Jan 1, 2025 = Wednesday. Jan 1, 2100 = Friday. Fun bet: ask a friend what day their 30th birthday will be — bet before you calculate.
Frequently asked questions
Leap years accounted for?
Yes — JavaScript Date handles Gregorian leap years correctly: Feb 29 only in years divisible by 4, except century years not divisible by 400.
Julian calendar dates (pre-1582)?
We use Gregorian for all dates retroactively. Add 10 days (1500s) to 13 days (1900s) to convert Julian → Gregorian. Russia switched in 1918.
Same worldwide?
Yes — Monday in New York is Monday in Tokyo. Day of week is universal.
Negative diff?
Future dates show negative because "days since today" is negative — we flip the wording to "days from now".
Zeller's formula?
Zeller's is a manual algorithm; we use JS Date. Same result, fewer bugs.
Last updated
For general calculations only. Not financial, tax, or legal advice — see our disclaimer.