Day of the week calculator
Pick a date to see which day of the week it falls on. It works for birthdays, anniversaries, historic dates and dates far in the future.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Choose a date with the date picker or type it in.
- Read the day of the week. Below it you see the ISO weekday number and the calendar the date was counted in.
- Change the date to check another one; the result updates at once.
How it works
Every date has a day number counted from a fixed point, and the weekdays repeat every 7 days. So the weekday is the day number modulo 7, shifted to the right starting day. The tool uses the Gregorian calendar for every date. From 15 October 1582, when the calendar was introduced, this matches what people used; for earlier dates it is the proleptic Gregorian calendar, the same rules applied backwards.
Worked examples
- 3 November 2026 is a Tuesday (ISO weekday 2).
- 1 January 2000 was a Saturday.
- 20 July 1969, the Apollo 11 landing, was a Sunday.
- 15 October 1582, the first day of the Gregorian calendar, was a Friday.
Good to know
Leap days are handled by the full Gregorian rule: 2000 and 2024 had a 29 February, 1900 and 2100 do not. Dates are plain calendar days, so time zones do not change the weekday.
Frequently asked questions
How do I find the day of the week for a date?
Pick the date in the field. The calculator counts the days from a fixed reference date and takes the remainder after dividing by 7, which gives the weekday without any lookup table.
Is the result right for dates before 1582?
It is right for the proleptic Gregorian calendar, which extends today's calendar backwards. Countries still used the Julian calendar then, so a document of the time may be dated up to ten days differently. The tool tells you which calendar it used.
When did people switch to the Gregorian calendar?
The first countries switched on 15 October 1582, the day after Thursday 4 October in the Julian calendar. Other countries followed over the next centuries, so historic dates from those places need conversion first.
Why is the weekday number shown as well?
ISO 8601 numbers the days from Monday = 1 to Sunday = 7. Spreadsheets, databases and programming languages often use this number or a variant where Sunday is 0.