How to Find the Day of the Week for Any Date in Your Head
Which day of the week was a given date, or which will it be? A calendar answers it, but there is a quick mental method that works for any date in the Gregorian calendar. It was devised by the mathematician John Conway and is known as the doomsday method.
The idea is that in every year, a set of easy-to-remember dates all fall on the same weekday, called that year's doomsday. Find the doomsday, then count from the nearest anchor date to your target. It takes a little practice, and each step is plain arithmetic.
The anchor dates
These dates always share a weekday within the same year:
| Months | Anchor dates |
|---|---|
| Even months from April | 4 April, 6 June, 8 August, 10 October, 12 December (4/4, 6/6, 8/8, 10/10, 12/12) |
| The 5/9 pair | 9 May and 5 September (5/9 and 9/5) |
| The 7/11 pair | 11 July and 7 November (7/11 and 11/7) |
| March | 14 March (3/14), which is two weeks after the last day of February |
| February | 28 February, or 29 February in a leap year |
| January | 3 January, or 4 January in a leap year |
In 2026, all of these fall on a Saturday. In 2024 they all fell on a Thursday. Pick the anchor closest to your target date and you will rarely count more than a week.
Step 1: find the year's doomsday
Number the weekdays from Sunday = 0 to Saturday = 6. Each century has an anchor weekday:
| Century | 1800s | 1900s | 2000s | 2100s |
|---|---|---|---|---|
| Anchor weekday | Friday (5) | Wednesday (3) | Tuesday (2) | Sunday (0) |
Take the last two digits of the year, YY, and work out three small numbers: a is YY ÷ 12 rounded down, b is the remainder of that division, and c is b ÷ 4 rounded down.
doomsday = (century anchor + a + b + c) mod 7mod 7 means keep the remainder after dividing by 7.
Worked example, 2026: the anchor for the 2000s is Tuesday = 2. YY = 26, so a = 2, b = 2 and c = 0. The sum is 2 + 2 + 2 + 0 = 6, which is Saturday. So 4 April, 6 June, 10 October and the other anchors in 2026 are all Saturdays.
Step 2: count from the nearest anchor
Find the anchor date nearest your target, note the gap in days, and move that many weekdays on from the doomsday. Only the remainder after dividing the gap by 7 matters.
Worked example, 19 October 2026: the nearest anchor is 10 October, a Saturday. 19 is 9 days later, and 9 = 7 + 2, so move 2 weekdays on from Saturday: Sunday, then Monday.
Worked example, 20 July 1969 (the date of the first Moon landing): the anchor for the 1900s is Wednesday = 3. YY = 69, so a = 5 (69 ÷ 12 = 5 remainder 9), b = 9 and c = 2 (9 ÷ 4 rounded down). The sum is 3 + 5 + 9 + 2 = 19, and 19 mod 7 = 5, so the doomsday is Friday. The nearest anchor is 11 July, a Friday. 20 July is 9 days later, so move 2 weekdays on from Friday, which gives Sunday.
If the target is before the anchor, count backwards. For example, 3 October 2026 is 7 days before 10 October, so it is also a Saturday.
Shortcuts and sanity checks
- The same date next year falls one weekday later, or two weekdays later when a 29 February lies in between. 19 October 2026 is a Monday and 19 October 2027 is a Tuesday. By 19 October 2028, after the leap day of 2028, it is a Thursday.
- A common year is 365 days, which is 52 weeks and 1 day, so the weekday advances by one. A leap year is 52 weeks and 2 days, so it advances by two.
- Between 1901 and 2099 the whole calendar repeats every 28 years, because no century leap-day exception falls in that window. 1 January 2026 and 1 January 2054 are both Thursdays.
- Over a full 400-year cycle the Gregorian calendar repeats exactly, including weekdays.
A common source of mistakes is applying the method to dates before the Gregorian calendar was adopted. Weekday names continued in an unbroken seven-day cycle when the calendar changed, but the dates did not: in 1582 in Catholic countries, Thursday 4 October was followed by Friday 15 October. The method as given here only works for dates counted in the Gregorian calendar.
Practice, and when to use a tool
Start by memorising the century anchors and the six anchor patterns, then practise on dates you can verify, such as birthdays. Within a week or two, most people can do it in a few seconds. For one-off checks, or when accuracy matters, the day of the week calculator gives the answer immediately, and the calendar calculator shows the whole month around it. To see how many days separate two dates, try the days between dates calculator.
- Day of the Week Calculator: Pick a date and see whether it is a Monday, a Friday or any other day of the week. The guide shows how to work it out by hand with a simple formula.
- Calendar Calculator: Two date tools in one: move a date forward or back by any mix of years, months, weeks and days, or measure how long it is from one date to another.
- Days Calculator: Use the days calculator to find how many days lie between two dates, or to add days to a date and see the result with its day of the week. Weekdays, weeks and months are reported too.
This article is general information, not professional advice. See our Disclaimer and Editorial Policy.
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