What day of the week is a given date?
To find the day of the week for any date, mathematicians have developed several elegant algorithms. Zeller's congruence uses modular arithmetic to compute the day directly from the day, month, and year values. The Doomsday algorithm, invented by mathematician John Conway, exploits the fact that certain memorable dates (4/4, 6/6, 8/8, 10/10, 12/12, and others) always fall on the same day of the week within a given year — making mental calendar calculations possible. For everyday use, our calculator does all of this automatically: just enter any date from 1900 to 2100 and instantly see which day of the week it falls on, along with the ISO week number, the day of the year, and how many days remain in the year.
How many days are in each month?
January, March, May, July, August, October, and December have 31 days. April, June, September, and November have 30 days. February has 28 days in a regular year and 29 days in a leap year. A leap year occurs in every year divisible by 4, except for century years (divisible by 100) which must also be divisible by 400 to be leap years. So 2000 was a leap year, but 1900 was not. This cycle means the day-of-week pattern for any given date shifts by one or two days each year, which is why the same date falls on a different weekday year after year.
Frequently asked questions
What day is it today?
Open this page to see today's day of the week displayed automatically. The date shown is based on your local time zone. No input is needed — the result updates instantly when you load the page.
What day was January 1, 2000?
January 1, 2000 was a Saturday. This was also the first day of the new millennium (or, by strict counting, the second-to-last year of the 20th century). You can verify this by entering 01/01/2000 in the date field above.
What day of the week is my birthday?
Enter your birth date in the field above and the calculator will tell you which day of the week you were born. You can also check what day your next birthday will fall on by entering the upcoming year with your birth month and day.
What day will it be in 100 days?
For that calculation, use our Date Calculator tool which lets you add days to a date. Enter today's date, choose "Add 100 days", and get the exact future date along with its day of the week.
What is the Doomsday algorithm?
The Doomsday algorithm is a mental math method invented by John Conway that lets you calculate the day of the week for any date in your head. It works by memorizing that certain anchor dates in each year (called Doomsdays) always fall on the same weekday. For 2026, the Doomsday is Monday. Once you know the Doomsday, you can compute any other date relative to it.
What day will Christmas be in 2026?
Christmas 2026 (December 25, 2026) falls on a Friday. Enter 25/12/2026 above to confirm. Christmas falls on a Friday in 2026, then on a Saturday in 2027, and on a Monday in 2028 (a leap year).
What day was a date in the past?
Enter any historical date between January 1, 1900 and December 31, 2100 in the date field above. The calculator uses the Gregorian calendar for all dates in that range and returns the correct day of the week instantly.
What day of the week is my next birthday?
Enter your upcoming birthday (current year and your birth month and day) in the date field. The result shows the exact day of the week. For example, if your birthday is June 15, enter 15/06/2026 to see it falls on a Monday.