Day of the Week Calculator
Find the weekday of any date from year 1 to 9999, with Zeller and Doomsday working shown, Julian calendar support and a fourth-Thursday style date finder.
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About this toolWhat is the Day of the Week Calculator?
Enter a day, month and year and the Day of the Week Calculator tells you the weekday it fell on or will fall on, with the full working. 20 July 1969 was a Sunday, 4 July 1776 was a Thursday, and 25 December 2026 is a Friday. You also get the day of the year, the ISO week date, how many days away the date is, and the Julian Day Number astronomers and programmers use as a universal day count.
Under the answer the tool shows two methods you can repeat with a pencil: Zeller's congruence, with every term filled in, and John Conway's Doomsday rule, with the century anchor, the year's doomsday and the nearest memorable date. A strip of the same date in the coming ten years shows when your birthday or anniversary next lands on a weekend.
For history, switch the calendar to Julian, or to "Julian before 1582" to follow the Catholic switchover automatically. A second panel finds dates such as the fourth Thursday of November or the last Monday of May for any year.
- Weekday for any date from year 1 to 9999
- Gregorian, Julian or automatic switch at 15 October 1582
- Zeller's congruence and Doomsday working shown
- Julian Day Number, day of year, ISO week date and days from today
- Nth weekday of a month finder and a ten-year weekday strip
How to use the Day of the Week Calculator
- Type the day and year and choose the month. Use today fills in the current date.
- Leave the calendar on Gregorian for modern dates. For a historical date, choose Julian, or Julian before 1582 to switch automatically on 15 October 1582.
- Read the weekday and its position in the month, such as "the 4th and last Thursday of November 2026".
- Expand your understanding with the Zeller and Doomsday working, and check the coming years strip for weekends.
- To find a floating holiday, set which weekday, which occurrence, the month and the year in the finder, then press Show to load it.
Worked examples
The Moon landing
Input
20 July 1969, Gregorian
Output
Sunday; Zeller h = 225 mod 7 = 1 (Sunday); Doomsday 1969 = Friday, 11 July is a doomsday, so the 20th is 9 days later: Sunday
The anchor for the 1900s is Wednesday. 69 = 5 x 12 + 9, with two 4s in 9, so 3 + 5 + 9 + 2 = 19, which is 5 mod 7: Friday.
A date from colonial America
Input
2 September 1752, Julian
Output
Wednesday; Gregorian equivalent 13 September 1752
This was the last Julian day in Britain and its colonies. The next morning was Thursday 14 September in the new calendar, eleven day numbers later.
US Thanksgiving
Input
Fourth Thursday of November 2026
Output
Thursday 26 November 2026
1 November 2026 is a Sunday, so the first Thursday is the 5th and the fourth is the 26th.
Background and insight
The modern Gregorian calendar was introduced by Pope Gregory XIII so that Thursday 4 October 1582 (Julian) was followed by Friday 15 October 1582. The weekday cycle was never interrupted; only the day numbers jumped. Britain and its colonies, including the future United States, kept the Julian calendar until 1752, when Wednesday 2 September was followed by Thursday 14 September. Russia switched in 1918 and Greece in 1923. A date written in an old document therefore needs to be read in the calendar its author used, which is why the tool offers both.
Zeller's congruence, published by Christian Zeller in the 1880s, treats January and February as months 13 and 14 of the previous year so that the leap day falls at the end of the counting year. With q the day, m the month, K the year within the century and J the century, the Gregorian form is h = (q + floor(13(m+1)/5) + K + floor(K/4) + floor(J/4) + 5J) mod 7, where h = 0 is Saturday. The Julian form replaces the last two terms with 5 + 6J.
Conway's Doomsday rule relies on the fact that certain easy dates always share a weekday within a year: 4/4, 6/6, 8/8, 10/10, 12/12, 9/5, 5/9, 7/11, 11/7, the last day of February and 14 March. Find that weekday for the year from a century anchor (Tuesday for the 2000s, Wednesday for the 1900s) plus a quick calculation on the last two digits, then count from the nearest doomsday. The calculator checks both methods against a Julian Day Number calculation, so all three always agree.
Common use cases
Birthdays and anniversaries
See what day you were born on, and which coming years put a birthday, wedding anniversary or holiday on a weekend.
Genealogy and history
Check weekdays in old records, letters and diaries, including dates written in the Julian calendar before the switch.
Planning floating holidays
Find dates defined by rule, such as Thanksgiving, Memorial Day, Labor Day or the second Sunday of May.
Teaching and mental maths
Practise Zeller's congruence and the Doomsday rule with the working laid out step by step.
Tips and limitations
- A date moves forward one weekday each year, and two when a 29 February falls in between.
- Gregorian dates before 1582 are "proleptic": the rules extended backwards. Historians usually quote such dates in the Julian calendar.
- Dates between 5 and 14 October 1582 exist only in the Julian calendar; in "Julian before 1582" mode they are read as Julian.
- Year 1 is the first year the tool accepts. There is no year 0 in the historical BC/AD count.
Frequently asked questions
What day of the week was I born on?
Enter your date of birth and the calculator returns the weekday together with the working. Someone born on 15 May 1990, for example, was born on a Tuesday.
How does the Doomsday rule work?
Each year, 4/4, 6/6, 8/8, 10/10, 12/12, 9/5, 5/9, 7/11, 11/7, 14 March and the last day of February share one weekday, the doomsday. Work it out from the century anchor and the year's last two digits, then count from the nearest of those dates to yours.
Is Zeller's congruence accurate for every date?
Yes, for the calendar it is written for. The Gregorian and Julian forms differ in their century terms, so use the form that matches the calendar the date was written in. The tool cross-checks Zeller against a Julian Day Number for every answer.
Why were 11 days missing in September 1752?
Britain and its colonies moved from the Julian to the Gregorian calendar that year. By then the calendars differed by 11 days, so Wednesday 2 September was followed by Thursday 14 September. The weekday sequence did not break.
Which calendar should I use for dates before 1582?
Historical records from before 1582 are almost always Julian, so choose Julian. "Proleptic Gregorian" dates are mainly used in astronomy and software; the tool supports both.
How can I find the nth weekday of a month, like Thanksgiving?
Use the finder: choose Fourth, Thursday, November and the year. For 2026 it returns 26 November. "Last" is also available, for rules like the last Monday of May.
What is a Julian Day Number?
A continuous count of days used in astronomy, starting from noon on 1 January 4713 BC in the Julian calendar. 1 January 2000 is JDN 2,451,545. Subtracting two JDNs gives the days between dates in any calendar.
Is there an in-depth guide to the Day of the Week Calculator?
Yes. “How to Find the Day of the Week for Any Date, by Hand” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
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