Day of the Week Calculator
Find which day of the week a given date falls on.
| Date |
Result
The day of the week will appear here.
Method: Zeller’s congruence
For the Gregorian calendar, Zeller’s congruence computes the day of the week from the day, month, and year:
h = (q + ⌊13(m+1)/5⌋ + K + ⌊K/4⌋ + ⌊J/4⌋ + 5J) mod 7
where q is the day of month, m is the month (March=3 … January=13, February=14 of the previous year), K = year mod 100, and J = ⌊year/100⌋. The result maps to days of the week (with Saturday = 0 in Zeller’s original form; this calculator displays the weekday name directly).
Notes
This calculator uses the Gregorian calendar (the calendar in common civil use today). It validates that the date is a real calendar date, including leap years (a year is a leap year if divisible by 4, except century years not divisible by 400).
How it works
This finds the weekday for a given calendar date using a calendar algorithm (Zeller’s congruence) and accounts for leap years in the Gregorian calendar.
Formula (Zeller’s congruence)
- For month m, day d, year y (with Jan/Feb treated as months 13/14 of the previous year): h = (d + ⌊13(m+1)/5⌋ + K + ⌊K/4⌋ + ⌊J/4⌋ + 5J) mod 7, where K=year mod 100, J=⌊year/100⌋.
Worked example
2026-11-10 falls on a Tuesday. 2000-02-29 (a leap day) was a Tuesday.
For general information only. Historical calendar reforms mean very old dates may differ by calendar system.
How to use the Day of the Week Calculator
It takes a few seconds, and every figure is calculated in your browser.
- Enter the date.
- Press Calculate — the result appears in the dark panel beside the form.
- Use Copy, CSV, Share or Print under the result if you want to keep it.
Day of the Week Calculator — frequently asked questions
What formula does the Day of the Week Calculator use?
For the Gregorian calendar, Zeller’s congruence computes the day of the week from the day, month, and year: h = (q + ⌊13(m+1)/5⌋ + K + ⌊K/4⌋ + ⌊J/4⌋ + 5J) mod 7 where q is the day of month, m is the month (March=3 … January=13, February=14 of the previous year), K = year mod 100, and J = ⌊year/100⌋. The result maps to days of the week (with Saturday = 0 in Zeller’s original form; this calculator displays the weekday name directly).
How does the Day of the Week Calculator work?
This finds the weekday for a given calendar date using a calendar algorithm (Zeller’s congruence) and accounts for leap years in the Gregorian calendar.
What assumptions and limitations should I know about?
This calculator uses the Gregorian calendar (the calendar in common civil use today). It validates that the date is a real calendar date, including leap years (a year is a leap year if divisible by 4, except century years not divisible by 400).
Can you walk through a worked example?
2026-11-10 falls on a Tuesday. 2000-02-29 (a leap day) was a Tuesday.
Last updated 10 November 2026 · Formula, worked example and assumptions are documented above, and every result is calculated in your browser.