How to use the day of the week calculator
Choose a date with the date picker or type it in. The big box shows the weekday — the answer to “what day of the week was I born?” or “what day is Christmas next year?” — and the details below add the day of the year, the ISO week number, the number of days from today, and the next year whose calendar is identical. The table lists the same month and day in other years, so you can see at a glance which year your birthday or anniversary falls on a weekend.
Why the weekday moves each year
A common year has 365 days, which is 52 weeks plus 1 day, so a date usually moves forward one weekday from one year to the next: Christmas 2025 was a Thursday and Christmas 2026 is a Friday. After a leap day (February 29) it moves two. The Gregorian calendar adds a leap day every fourth year, except century years not divisible by 400 — 1900 was not a leap year, 2000 was. Over a full 400-year cycle there are exactly 146,097 days, which is precisely 20,871 weeks, so the whole calendar repeats every 400 years. A side effect: the 13th of a month lands on a Friday slightly more often than on any other weekday — 688 times every 400 years.
The Doomsday method: do it in your head
Mathematician John Conway devised a quick way to find any weekday mentally. Certain easy-to-remember dates always fall on the same weekday within a year — that year’s “doomsday”:
- 4/4, 6/6, 8/8, 10/10 and 12/12
- 5/9 and 9/5, 7/11 and 11/7 (“working 9 to 5 at the 7-Eleven”)
- March 14 (Pi Day) and the last day of February
- January 3 in common years, January 4 in leap years
Each century has an anchor: Wednesday for the 1900s and Tuesday for the 2000s. To get a year’s doomsday, take the last two digits, divide by 12, and add the quotient, the remainder, and the remainder divided by 4 (whole part) to the anchor. For 2026: 26 = 2 × 12 + 2, and 2 ÷ 4 = 0, so Tuesday + 2 + 2 + 0 = Saturday. December 12 is a doomsday, and December 25 is 13 days later — Saturday plus 13 days (one week and six days) is Friday. The calculator shows these steps for whatever date you choose.
Famous dates
| Date | Event | Weekday |
|---|---|---|
| July 4, 1776 | US Declaration of Independence adopted | Thursday |
| May 8, 1945 | Victory in Europe (VE) Day | Tuesday |
| July 20, 1969 | Apollo 11 Moon landing | Sunday |
| November 9, 1989 | Fall of the Berlin Wall | Thursday |
| January 1, 2000 | First day of 2000 | Saturday |
| September 11, 2001 | September 11 attacks | Tuesday |
ISO week numbers
Many countries, especially in Europe, number the weeks of the year. Under ISO 8601, weeks start on Monday and week 1 is the week that contains the year’s first Thursday (equivalently, the week with January 4). So the first days of January can belong to the last week of the previous year: January 1, 2000 was in week 52 of 1999. The calculator writes the week as year-W-number, such as 2026-W42. To see today’s week number, open today’s date.
Old dates and calendar changes
The calculator uses the Gregorian calendar for every date, extended backward before it existed (the proleptic Gregorian calendar). Countries switched from the Julian calendar at different times — Catholic Europe in 1582, Britain and its American colonies in 1752, Russia in 1918, Greece in 1923 — and dates written before the switch are usually Julian. For those, the weekday here will not match a contemporary record. For counting days between two dates, use the date difference calculator; to find the date a number of days from now, use add days to a date.
Frequently asked questions
What day of the week was I born?
Enter your date of birth above; the big box shows the weekday. The table underneath lists the same day in the following years, so you can also see which of your birthdays fall on a weekend.
How do I work out the day of the week without a calculator?
Use the Doomsday method: find the year’s doomsday from the century anchor and the last two digits, then count from the nearest easy date such as 4/4, 6/6, 8/8, 10/10 or 12/12. The result box shows the full working for your date.
When does a year have the same calendar as another?
Two years share a calendar when they start on the same weekday and are both leap or both common years. A common year usually repeats after 6 or 11 years and a leap year after 28 (for example 2026 and 2037, 2024 and 2052). The calculator shows the next matching year.
What is the ISO week number?
It is the week of the year under the international standard ISO 8601: weeks run Monday to Sunday and week 1 contains the first Thursday of January. Most years have 52 weeks; some, like 2020 and 2026, have 53.
Last updated: October 14, 2026