It is a fun question with a surprisingly clever answer: what day of the week were you born? Maybe you have heard the old rhyme, Monday’s child is fair of face, and want to know which line is yours. The quickest way is a date or age calculator, but there is also a beautiful hand method, the Doomsday algorithm, that mathematicians use to work out the weekday of any date in their head. This guide explains the easy way, introduces the Doomsday method with a worked example, and shows how the same idea reveals the weekday of any past or future date. To get your answer instantly along with your exact age, use our age calculator.
Quick answer: The easiest way to find what day of the week you were born is a date or age calculator that shows the weekday for any date. To do it by hand, mathematicians use the Doomsday algorithm, which anchors each year to a known reference weekday and counts from there.
The easy way
For a guaranteed correct answer in seconds, enter your date of birth into a date or age calculator. It applies the calendar rules exactly, including leap years, and tells you the weekday. This is the method to use if you just want the answer rather than the mental exercise.
If you enjoy a puzzle, though, the Doomsday algorithm lets you work it out yourself.
The Doomsday method
The Doomsday algorithm, devised by mathematician John Conway, is based on the fact that within any given year, several easy-to-remember dates all fall on the same weekday, called that year’s doomsday. These include the 4th of April (4/4), 6th of June (6/6), 8th of August (8/8), 10th of October (10/10), and 12th of December (12/12), plus the 11th of July (7/11) and the last day of February.
Once you know the doomsday weekday for a year, you can count forward or backward from one of these anchor dates to any date in that year.
A worked example
Suppose you were born on 4 July 2000. The doomsday for the year 2000 is Tuesday.
- Find a nearby anchor date: 11 July (7/11) is a doomsday, so it is a Tuesday.
- Count back from 11 July to 4 July: that is exactly 7 days, one week.
- Since 4 July is a whole week before a Tuesday, it is also a Tuesday.
In plain English: 4 July 2000 was a Tuesday. The trick is always to hop to the nearest anchor date whose weekday you know, then count the days to your target.
Get your birth day instantly
Skip the mental maths: our age calculator shows the weekday you were born along with your exact age, and our date difference calculator works out the days between any two dates.
Anchor days by century
Each century has a base weekday, called the anchor day, that the Doomsday method builds on:
| Century | Anchor day |
|---|---|
| 1800s | Friday |
| 1900s | Wednesday |
| 2000s | Tuesday |
| 2100s | Sunday |
From the century anchor, a further small calculation gives that specific year’s doomsday. Most people find it easier to simply remember that 2000 was a Tuesday and use a calculator for other years.
The days-of-the-week rhyme
Once you know your day, there is a traditional rhyme that assigns a trait to each: Monday’s child is fair of face, Tuesday’s child is full of grace, Wednesday’s child is full of woe, Thursday’s child has far to go, Friday’s child is loving and giving, Saturday’s child works hard for a living, and the child born on Sunday is bonny and blithe. It is folklore, of course, but a charming way to round off the answer.
Frequently asked questions
How do I find out what day of the week I was born?
The simplest way is to enter your date of birth into a date or age calculator, which applies the calendar rules and shows the weekday instantly. To work it out by hand, use the Doomsday algorithm: find the year’s doomsday weekday, then count from a known anchor date like 4/4 or 12/12 to your birth date.
What is the Doomsday algorithm?
The Doomsday algorithm, created by mathematician John Conway, is a method for finding the weekday of any date. It relies on the fact that certain dates, such as 4/4, 6/6, 8/8, 10/10, and 12/12, all fall on the same weekday in a given year, called the doomsday. From there you count to any date.
What day of the week was 4 July 2000?
The 4th of July 2000 was a Tuesday. The doomsday for the year 2000 is Tuesday, and 11 July is a doomsday anchor date, also a Tuesday. Since 4 July is exactly one week before 11 July, it falls on the same weekday, Tuesday. A calculator confirms this instantly.
Is there a formula for the day of the week?
Yes. Besides the Doomsday algorithm, mathematicians use Zeller’s congruence, a formula that calculates the weekday from the day, month, and year using modular arithmetic. Both give the same result. For everyday use, a date calculator is far simpler, but the formulas are elegant ways to do it by hand.
Why does the day of the week for a date change each year?
Because a year is 365 days, which is 52 weeks plus one extra day (two in a leap year). That leftover day shifts a fixed date forward by one weekday each year, and by two across a leap year. This is why your birthday lands on a different day of the week from one year to the next.
The bottom line
To find what day of the week you were born, the easy route is a date or age calculator. For the clever route, use the Doomsday algorithm: know the year’s doomsday, such as Tuesday for 2000, then count from an anchor date like 11 July to your birthday, which is how 4 July 2000 works out as a Tuesday. Get your birth day and exact age at once with our age calculator.
Further reading
For authoritative background on this topic, see Determination of the day of the week on Wikipedia.
Note. This article is for general informational and educational purposes. The days-of-the-week rhyme is folklore, not fact.
Last reviewed: July 2026