Day of the Week Calculator
Find what day of the week any date falls on — past, present or future. Works for any date in the Gregorian calendar.
How to use the Day of the Week Calculator
- Enter your inputs into the Day of the Week Calculator above.
- Results update instantly as you type — no submit button needed.
- Adjust any value to see how the result changes in real time.
The Zeller's congruence
h = (q + ⌊13(m+1)/5⌋ + K + ⌊K/4⌋ + ⌊J/4⌋ − 2J) mod 7
q = day of month, m = month (with Jan = 13 and Feb = 14 of previous year), K = year mod 100, J = century. Result h: 0 = Saturday, 1 = Sunday, 2 = Monday, ..., 6 = Friday.
Worked example
2026-05-26: Tuesday. 2000-01-01: Saturday. 1969-07-20 (Apollo 11 moon landing): Sunday. Your birth date: try it and see.
Frequently asked questions
Does this work for any year?
For Gregorian calendar dates (1582 onwards in most of Europe; varying adoption elsewhere). Pre-Gregorian dates require Julian calendar conversion first.
Are all months/days possible?
February 29 only exists in leap years. December 31 exists in every year. Day-of-week distributions are uniform over long enough periods.
What's the most common birthday day?
In the US, Tuesday (slight statistical edge due to scheduled inductions and C-sections being most common Tuesday–Thursday). Otherwise weekday distribution is roughly uniform.