The fastest way to find the day you were born is to enter your date of birth in our what day was it tool. If you would rather work it out yourself, the doomsday rule lets you find the weekday of any date in your head in under a minute. For example, 14 August 1947, the date Pakistan celebrates as its independence day, was a Thursday.
The idea behind the doomsday rule
In any year, certain easy-to-remember dates all fall on the same weekday. That weekday is called the year’s “doomsday”. Once you know it, you count from the nearest of those dates to your birthday.
The memorable dates are:
- 4/4, 6/6, 8/8, 10/10, 12/12: 4 April, 6 June, 8 August, 10 October and 12 December.
- 9/5 and 5/9: 9 May and 5 September. 7/11 and 11/7: 11 July and 7 November. (A phrase to remember them: “working 9 to 5 at 7-Eleven”.)
- The last day of February (28th, or 29th in a leap year), and 14 March.
- 3 January in a normal year, or 4 January in a leap year.
Step 1: the century anchor
Each century has a starting weekday: Wednesday for 1900–1999, Tuesday for 2000–2099, and Friday for 1800–1899. Number the days Sunday = 0, Monday = 1, through Saturday = 6, so Wednesday is 3 and Tuesday is 2.
Step 2: the year’s doomsday
Take the last two digits of the year and call them yy. Then:
- a = how many whole 12s fit in yy.
- b = the remainder.
- c = how many whole 4s fit in b.
- Add the anchor + a + b + c and take the remainder after dividing by 7.
Worked example 1: 14 August 1947
yy = 47. a = 3 (36), b = 11, c = 2. Anchor for the 1900s is Wednesday (3). Total 3 + 3 + 11 + 2 = 19, and 19 ÷ 7 leaves 5, which is Friday. So the doomsday for 1947 is Friday, meaning 8 August 1947 was a Friday. Six days later, 14 August, was a Thursday.
Worked example 2: 23 March 1990
yy = 90. a = 7 (84), b = 6, c = 1. Total 3 + 7 + 6 + 1 = 17, which leaves 3: Wednesday. The nearest doomsday date is 14 March, a Wednesday. Nine days later is 23 March: Wednesday plus 2 (after removing a full week) is Friday.
Worked example 3: 8 October 2005
yy = 05. a = 0, b = 5, c = 1. Anchor for the 2000s is Tuesday (2). Total 2 + 0 + 5 + 1 = 8, leaving 1: Monday. 10 October 2005 was a Monday, so 8 October, two days earlier, was a Saturday.
An easier method for recent dates
If you know what weekday your birthday falls on this year, you can count back. Each year a date moves one weekday later, or two if a 29 February falls in between. For example, 23 March 2026 is a Monday. Going back one year moves it one weekday earlier: 23 March 2025 was a Sunday. This is quick for the last few years but error-prone for a birth date decades ago, where the doomsday rule is better. Leap years are covered in leap years explained.
Common slips
- Forgetting the leap-year versions of the January and February doomsdays.
- Counting the wrong way when your date is before the nearest doomsday date.
- Using the wrong century anchor for dates from 2000 onwards.
Once you know your birth weekday, you might like to see your exact age in days and weeks with our age calculator, or find the weekday of a famous date such as 29 February. For counting the gap between two dates, see how to count days between dates.
Frequently asked questions
How can I find what day I was born?
Enter your date of birth in a weekday finder such as our what day was it tool, or use the doomsday rule to work it out in your head.
What day of the week was 14 August 1947?
14 August 1947 was a Thursday. Pakistan’s independence is celebrated on 14 August each year.
Does the doomsday rule work for any year?
Yes, for any date in the Gregorian calendar, as long as you use the right century anchor. For dates before a country adopted the Gregorian calendar, results may not match old records.
Why does my birthday move to a different day each year?
A year is 52 weeks and 1 day, so dates move one weekday later each year, and two after a leap day.