Calculation method
Once year, month and day are fixed, the weekday is deterministic calendar arithmetic. The same valid Gregorian date always produces the same weekday.
🗓️ DAY OF WEEK
What day of the week was that date?
Birthdays, old memories, future plans — find the weekday instantly.
THAT DATE WAS / WILL BE
Day of year
Week number*
Leap year?
Date
*ISO week number.
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METHOD & INTERPRETATION
Day of the Week Calculator
Find the weekday for a valid Gregorian calendar date and see related calendar details without needing an external lookup.
Reading the output
Use it for birthdays, historical dates, anniversaries or planning. Very old historical dates may need caution because local civil calendars were not always Gregorian.
Worked example
1 January 2000 returns Saturday, a useful known reference for checking a weekday calculator.
Good to know
How weekday calculation works →This is exact for the stated Gregorian date; historical calendar conversion is a separate problem.