How do you calculate the day of the week for any date?

Use Zeller's congruence or the Doomsday method. Zeller: treat January and February as months 13 and 14 of the previous year, then h = (q + ⌊13(m+1)/5⌋ + K + ⌊K/4⌋ + ⌊J/4⌋ + 5J) mod 7, where q is the day, m the month, K the year within the century and J the century; h = 0 is Saturday, 1 Sunday, … 6 Friday. The calculator shows every step for your date.

What is the Doomsday method?

John Conway's mental method. In any year, 4/4, 6/6, 8/8, 10/10, 12/12, 5/9, 9/5, 7/11, 11/7, March 14 and the last day of February fall on the same weekday, the year's "doomsday". Find it from the century anchor (1800 Friday, 1900 Wednesday, 2000 Tuesday, 2100 Sunday) plus ⌊yy/12⌋ + (yy mod 12) + ⌊(yy mod 12)/4⌋, then count from the nearest doomsday to your date.

What day will it be 90 days from today?

Use Date math: the date field starts at today, so choose Add, enter 90 and Days. Because 90 = 12 weeks + 6 days, the weekday is always 6 days later in the week (or one day earlier), so a Saturday start gives a Friday.

How does adding a month to January 31 work?

The calculator keeps the day of the month and stops at the last valid day, so January 31 + 1 month is February 28, or February 29 in a leap year. February 29 + 1 year is February 28. This is the same rule most spreadsheet and calendar software uses.

What date range does this calculator support?

Years 100 through 9999 in the proleptic Gregorian calendar, which extends today's calendar backward.

Is the result right for dates before 1582 or 1752?

Only if the date was written in the Gregorian calendar. Most European dates before October 15, 1582, and British and American colonial dates before September 14, 1752, used the Julian calendar, which gives a different weekday. Use the Day of Week in History tool, which switches to the Julian calendar automatically.

Does it account for leap years?

Yes. A year is a leap year if it is divisible by 4, except century years, which must be divisible by 400. So 1900 was not a leap year but 2000 was, and 2100 will not be.

Does this tool send my data anywhere?

No. All calculations run in your browser.

Day of Week Calculator

Pick any date to see its weekday, its place in the month (for example the 2nd Saturday), how many days it is from today and the Zeller and Doomsday working. Then add or subtract days, weeks, months or years, or find a date such as the 4th Thursday of November.

To find the day of the week, the Doomsday method uses the fact that 4/4, 6/6, 8/8, 10/10, 12/12, 5/9, 9/5, 7/11, 11/7 and the last day of February always share one weekday each year.

Select a Date

Date picker

or enter manually

Month

Day

Year

Date math

Starts from the selected date.

Operation

Amount

Unit

Find a date

For example the 4th Thursday of November or the last Monday of May.

Which

Weekday

Month

Year

Enter a date on the left to see the day of the week and calendar view.

Doomsday dates by month

Every date in this table falls on the same weekday in a given year.

Month	Doomsday	Memory hook
January	Jan 3 (Jan 4 in leap years)	3rd in 3 years, 4th in the 4th
February	Feb 28 (Feb 29 in leap years)	last day of February
March	Mar 14	Pi Day; also "March 0" = last day of Feb
April	Apr 4	4/4
May	May 9	9-to-5 at 7-Eleven: 5/9
June	Jun 6	6/6
July	Jul 11	7/11
August	Aug 8	8/8
September	Sep 5	9/5
October	Oct 10	10/10
November	Nov 7	11/7
December	Dec 12	12/12

Century anchor days (Gregorian)

The doomsday of each century year; the pattern repeats every 400 years.

Years	Anchor day	Number
1700–1799	Sunday	0
1800–1899	Friday	5
1900–1999	Wednesday	3
2000–2099	Tuesday	2
2100–2199	Sunday	0
2200–2299	Friday	5

Anchor = (5 × (century mod 4) + 2) mod 7, with 0 = Sunday. Year doomsday = anchor + ⌊yy/12⌋ + (yy mod 12) + ⌊(yy mod 12)/4⌋, mod 7.

Researching a date written in the Julian calendar, before 1582 in Catholic Europe or 1752 in Britain and its colonies? Use the Day of Week in History calculator, which converts between the two calendars.

Quick answer

To find the day of the week, the Doomsday method uses the fact that 4/4, 6/6, 8/8, 10/10, 12/12, 5/9, 9/5, 7/11, 11/7 and the last day of February always share one weekday each year. For 2026 that weekday is Saturday: century anchor Tuesday (2), plus 26 ÷ 12 = 2 remainder 2, plus 2 ÷ 4 = 0, gives 2 + 2 + 2 + 0 = 6, Saturday. Count from the nearest doomsday to your date.

Examples

Question	Answer
What day is July 4, 2026?	Saturday (July 11 is a doomsday, 7 days earlier)
What day is December 25, 2026?	Friday (Dec 12 is Saturday, 13 days later)
What date is 90 days after October 10, 2026?	Friday, January 8, 2027
When is the 4th Thursday of November 2026?	November 26, 2026 (US Thanksgiving)

Enter a date above for its weekday and the full working, or use Date math to add days.

Summary

The Day of Week Calculator tells you which weekday any date falls on, from year 100 to 9999, and shows the arithmetic two ways: Zeller's congruence and John Conway's Doomsday method, so you can check it or learn to do it in your head. It also works as a quick date calculator: add or subtract days, weeks, months or years from the date and read the new weekday, see how many days the date is from today, and find a date by rule, such as the last Monday of May or the 4th Thursday of November. Dates use the Gregorian calendar throughout; for dates recorded under the Julian calendar before 1582 or 1752, use the Day of Week in History tool.

How it works

Enter a date with the date picker or type month, day and year. Today is filled in on load.
The weekday is computed from the Gregorian calendar and cross-checked with Zeller's congruence and the Doomsday method; both workings are shown step by step.
The result also gives the day of the year, ISO week, whether the year is a leap year, the date's place in the month (for example the 3rd Friday) and the number of days from today.
Under Date math, add or subtract a number of days, weeks, months or years. Month and year steps keep the day of the month and stop at the month's last day (January 31 + 1 month = February 28 or 29).
Under Find a date, choose 1st–5th or last, a weekday, a month and a year to get dates such as Thanksgiving or Memorial Day.

Use cases

Find out what day of the week you were born, or what day a birthday or anniversary lands on this year.
Work out what date and weekday it will be 30, 60 or 90 days from a given date, for deadlines and notice periods.
Find floating dates such as the 4th Thursday of November or the last Monday of May.
Learn the Doomsday method with a worked example for any date.
Check Zeller's congruence homework step by step.
Confirm whether a holiday or event falls on a weekday or a weekend.

Frequently Asked Questions

Last updated: 2026-10-10 · Reviewed by Nham Vu