Day of the week calculator
This day of the week calculator finds the weekday of any date: September 11, 2001 was a Tuesday and July 4, 1776 a Thursday. Enter a date to see the day instantly, with week number, day of the year and the working.
Source: U.S. Naval Observatory: Julian Date Converter (Julian/Gregorian calendar, October 1582). Updated: .
How it is calculated
How the weekday is calculated
The calculator counts days from a fixed starting point (the Julian Day Number used by the U.S. Naval Observatory) and divides by 7; the remainder gives the day of the week. As a working you can follow by hand it also shows Zeller’s congruence (Christian Zeller, 1887). With day q, month m, year of the century K and century J:
h = (q + ⌊13(m+1)/5⌋ + K + ⌊K/4⌋ + ⌊J/4⌋ + 5J) mod 7
gives a number from 0 (Saturday) to 6 (Friday). January and February count as months 13 and 14 of the previous year so that the leap day falls at the end of the counting year. Both methods agree; we checked every year from 1 to 9999.
The calendar change
Catholic countries switched from the Julian to the Gregorian calendar in October 1582; Britain and the American colonies followed in September 1752, when Wednesday, September 2 was followed by Thursday, September 14. The weekdays themselves never broke sequence. By default the tool uses the Julian calendar before October 15, 1582, so Columbus’s landfall on October 12, 1492 correctly comes out as a Friday. For English or colonial dates between 1582 and 1752, choose “always Julian”.
Examples
| Event | Date | Weekday |
|---|---|---|
| US Declaration of Independence | July 4, 1776 | Thursday |
| D-Day | June 6, 1944 | Tuesday |
| Moon landing | July 20, 1969 | Sunday |
| 9/11 attacks | September 11, 2001 | Tuesday |
The table below the result shows which weekday the date – your birthday, say – falls on in the coming years. For the number of days between two dates use the date calculator; for week numbers, the week number page.
Frequently asked questions
What day of the week was 9/11?
September 11, 2001 was a Tuesday.
What day of the week was I born?
Enter your date of birth above – May 15, 1990, for example, was a Tuesday. The table below also shows your birthday’s weekday for the next few years.
What day of the week was July 4, 1776?
July 4, 1776 was a Thursday (in the Gregorian calendar, which the American colonies had used since 1752).
How can I work out the day of the week in my head?
Use the Doomsday rule: certain dates (4/4, 6/6, 8/8, 10/10, 12/12) always share a weekday within a year – in 2026 it is Saturday. Count forward or back from there.
Is the weekday right for dates before 1582?
Yes. The seven-day week ran on without interruption through the calendar reform. Older dates are calculated in the Julian calendar, or in the proleptic Gregorian calendar if you choose.
Sources and legal basis
- U.S. Naval Observatory: Julian Date Converter (Julian/Gregorian calendar, October 1582)
- Wikipedia: Zeller’s congruence
- ISO 8601 – Date and time format (week numbering)
As of:
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