Day of the Week Calculator (What Day Was It?)
Pick any date to see which day of the week it falls on.
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Day of the Week Calculator (What Day Was It?) by TheCalcTools
How the Day of the Week Calculator (What Day Was It?) works
Dates use the proleptic Gregorian calendar, the calendar in use today, extended backwards. The calculator counts days from a fixed reference date and takes the remainder after dividing by 7.
Countries switched from the Julian calendar on different dates (Britain and its colonies in 1752), so historical documents written before the switch may give a different weekday.
The formula
Worked example
Using the default values shown in the calculator:
| Date | 1990-07-15 |
|---|
- 15 July 1990 was a Sunday.
- It was day 196 of the year.
Result:
| Day of the week | Sunday |
|---|---|
| Full date | Sunday, 15 July 1990 |
| Day of the year | 196 |
| ISO week number | 28 |
| Days from 17 October 2026 | -13,243 |
Frequently asked questions
What day of the week was I born?
Enter your date of birth: the result shows the weekday. A date repeats on the same weekday every 5, 6 or 11 years depending on leap years.
Does it work for dates before 1900?
Yes, back to year 100, using the Gregorian calendar rules for every year.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.