Day of the week calculator

Weekdays repeat every 7 days, so the day of the week of any date is the number of days from a date whose weekday is known, divided by 7, with the remainder counted on from that weekday.

By hand, the doomsday method is the quickest. Every year has a doomsday, a weekday shared by 4/4, 6/6, 8/8, 10/10, 12/12, 5/9, 9/5, 7/11, 11/7 and the last day of February. The century sets a starting day: Sunday for the 1700s, Friday for the 1800s, Wednesday for the 1900s and Tuesday for the 2000s. Then take the last two digits of the year, divide by 12, and add the quotient, the remainder, and the remainder divided by 4, dropping fractions.

For 1776: 76 ÷ 12 = 6 remainder 4, and 4 ÷ 4 = 1, so 6 + 4 + 1 = 11, which is 4 past a multiple of 7. Four days after Sunday is Thursday, so 7/11 was a Thursday in 1776, and July 4, a week earlier, was a Thursday too.

For 2026: 26 ÷ 12 = 2 remainder 2, and 2 ÷ 4 rounds down to 0, so 2 + 2 + 0 = 4. Four days after Tuesday is Saturday, so 12/12/2026 is a Saturday, and Christmas, two weeks later, is a Friday.

The Gregorian calendar repeats every 400 years. That is 146,097 days, exactly 20,871 weeks, so a date 400 years on falls on the same weekday.

Dates before the Gregorian calendar was adopted are given in the Gregorian calendar extended backward. Britain and its colonies changed over in September 1752, so an English record from before then is dated in the Julian calendar, 11 days behind.