Day of the week calculator
The weekday of any date, past or future.
Day of the week
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Fill in the fields to see the result.
How it works
The date is converted to a count of days from a fixed starting point (1 January 1970, a Thursday). The remainder after dividing by 7 gives the weekday.
Dates use the Gregorian calendar throughout, including dates before it was adopted in 1582 and later in many countries. Historical records written in the Julian calendar may show a different weekday.
For ISO week numbers, see our sister site hourora.app.
Formula
Weekday = (days since 1 January 1970 + 3) mod 7, where 0 = Monday Leap year: divisible by 4, except centuries not divisible by 400
Worked example
19 October 2026 is a Monday, the third Monday of October. It is day 292 of 2026, which is not a leap year, so 73 days remain.
Questions people ask
Which years are leap years?
Years divisible by 4, except century years not divisible by 400. So 2000 and 2024 are leap years, but 1900 and 2100 are not.
Does this work for very old dates?
It works for years 1 to 9999 using the Gregorian calendar. Before a country adopted that calendar, local records used the Julian calendar and can differ by several days.
What does “occurrence in the month” mean?
It tells you which one of that weekday it is in the month, such as the 3rd Monday, which is useful for holidays set on a numbered weekday.