Day of the Week Calculator
Find the weekday for any date in history or the future.
How to use the Day of the Week Calculator
- Pick the date.
- Press Calculate. The result updates automatically as you type.
About the Day of the Week Calculator
Want to know the day of the week you were born, what day a holiday lands on next year, or whether a deadline falls on a weekend? Enter any date to see its weekday along with useful calendar facts: its day number within the year, how many days remain, its ISO week number and which quarter it belongs to.
Dates are calculated with the proleptic Gregorian calendar. For dates before a country adopted the Gregorian calendar (1752 in Britain and its colonies), historical records may show a different, Julian-calendar weekday.
Formula
The weekday can be found with Zeller's congruence (Gregorian calendar), treating January and February as months 13 and 14 of the previous year:
h = (q + ⌊13(m + 1) ÷ 5⌋ + K + ⌊K ÷ 4⌋ + ⌊J ÷ 4⌋ + 5J) mod 7
Here q is the day, m the month, K the year within the century and J the century; h = 0 is Saturday, 1 Sunday, … 6 Friday. The calculator uses the equivalent built-in calendar arithmetic.
Example calculation
Using the default values:
- Date = 1969-07-20
the calculator returns:
- Day of the week: Sunday
- Full date: Sunday, July 20, 1969
- Position in month: The third Sunday of July
- Day of the year: 201
- Days left in the year: 164
- ISO week number: 29
- Quarter: Q3
Frequently asked questions
What day of the week was July 20, 1969?
The Apollo 11 Moon landing on July 20, 1969 was a Sunday, the third Sunday of July.
Does the calendar repeat?
Yes. The Gregorian calendar repeats exactly every 400 years, and individual years repeat their layout every 5, 6 or 11 years (often 28 years for a full cycle).
How can I work out the weekday in my head?
Methods such as the Doomsday rule use memorable anchor dates (4/4, 6/6, 8/8, 10/10, 12/12) that always share the same weekday within a year.
Last updated: · Category: Time & Date calculators