Date math
Day of the Week Calculator
Enter any date to find out what day of the week it falls on.
Any date Past or future Instant
What is a Day of the Week Calculator?
A Day of the Week Calculator tells you which weekday — Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, or Sunday — any given date falls on. It works for birthdays, historical events, upcoming holidays, or any date you're curious about, past or future.
Because the calendar shifts by one day each year (two days after a leap year), the weekday for a fixed date like December 25 changes from year to year. This calculator does all the math automatically using the Gregorian calendar, so you get an instant, accurate answer without consulting a printed calendar.
Example: picking July 4, 1776 → Thursday — the day the United States adopted the Declaration of Independence.
How to Use the Day of the Week Calculator
Select any date from the date picker and click Find the Day. The result instantly shows which day of the week that date falls on, along with the full formatted date. Use the quick buttons to jump to today, tomorrow, or popular holidays.
The calculator supports any date from 1600 onward, correctly handling leap years, century rules, and Gregorian calendar transitions. For exact age calculations instead, see our Age Calculator.
Common Uses
- Birthday lookup – Find out what day of the week you were born on
- Wedding planning – Check which weekday a specific date falls on to plan ceremonies, rehearsals, or anniversaries
- History research – Determine the day of the week of historical events (e.g., the moon landing, treaties, battles)
- Event scheduling – Verify that a future date lands on the weekday you want
- Trivia and curiosity – Answer questions like "What day of the week was January 1, 2000?"
- Bible study / almanacs – Calculate historical weekdays for religious or genealogical research
How Day of the Week Works
The modern Gregorian calendar uses a 7-day week with a 400-year cycle of 146,097 days. Dividing 146,097 by 7 gives exactly 20,871 weeks — no remainder — which means the calendar pattern repeats every 400 years. Within that cycle, each year adds one day shift (two after a leap year) because 365 ÷ 7 leaves a remainder of 1.
Under the hood, the calculator uses JavaScript's built-in Date object, which
implements the Gregorian calendar rules
— including the "divisible by 4, except centuries not divisible by 400 are not leap years"
edge case. That means years like 1900 (not a leap year) and 2000 (leap year) are handled
correctly.
Frequently Asked Questions
What day of the week was I born on?
Enter your birth date into the calculator above to get the answer instantly. For reference: someone born on July 4, 1990 was born on a Wednesday; someone born on December 31, 1999 was born on a Friday.
How do you calculate the day of the week?
Several methods exist, including Zeller's congruence and the "Doomsday rule." Both are formulas that take year, month, and day as inputs and return a weekday number (0–6). This calculator uses JavaScript's Date object internally, which is fast and accurate for all Gregorian dates.
What day of the week is January 1?
It changes every year. In 2025, January 1 was a Wednesday. In 2026, it falls on a Thursday. Use the calculator above to check any year.
Can the calculator handle dates before 1900?
Yes, dates from 1600 onward (after the Gregorian calendar was adopted) work correctly. For dates before 1582 — when the Julian calendar was in use in many regions — the result uses a proleptic Gregorian calendar, which may differ from historical records.
Why does my birthday fall on a different weekday each year?
A standard year has 365 days = 52 weeks + 1 day. So your birthday's weekday advances by one each year. A leap year (366 days) advances by two, which is why birthdays after February 29 appear to "skip" a day the following year.
What day of the week is Christmas 2026?
Enter December 25, 2026 into the calculator to check. For a live Christmas countdown, visit our Days Until Christmas Calculator.