Introduction
The Day of the Week Calculator tells you what weekday any date falls on. Pick a month, day, and year, and it shows the answer right away — Monday, Tuesday, or any other day. It works for dates far in the past and far in the future, from 4713 BCE to 9999 CE.
You can choose the Gregorian calendar (New Style), which most of the world uses today, or the Julian calendar (Old Style), used in older records. If you are reading an old document with a split year like "1623/24," you can enter that too, and the tool will sort it out for you.
Along with the weekday, you get a full breakdown: the step-by-step math, a month calendar with your date marked, the day of the year, the ISO week number, the leap year rule, the season, the zodiac sign, and the Julian Day Number. A chart also shows how often that same date lands on each weekday over a 40-year span.
Use it to find your birth day of the week, check a wedding date, plan an event, or study history. Just type a date and hit Calculate. If you need the gap between two dates instead, try the Date Duration Calculator, or use the Age Calculator to turn a birth date into an exact age.
How to use our Day of the Week Calculator
Enter any date — month, day, and year — and the calculator tells you what day of the week it falls on. You also get the day of the year, ISO week number, leap year check, season, zodiac sign, Julian Day Number, a monthly calendar, and a step-by-step solution.
Month: Pick the month of your date from the drop-down list.
Day of Month: Type the day number, from 1 to 31. The tool checks that the day really exists in that month and year.
Year: Type the year, from −4713 to 9999. For BCE years, use 0 or a negative number (0 means 1 BCE).
Split-Year Digits (optional): Old records sometimes write a year two ways, like 1623/24. Put 1623 in the Year box and 24 here. This only changes dates from January 1 to March 24.
Calendar System: Choose Gregorian (New Style) for modern dates. Choose Julian (Old Style) for older records, such as English dates before September 14, 1752.
Hemisphere: Pick Northern or Southern so the season shown matches your part of the world.
Calculate, Reset, and Use Today: Press Calculate to see your answer. Press Reset to go back to the sample date, or press Use Today to load today's date.
Once you have the weekday, you can keep going: the Date Add Calculator shifts a date forward or back, the Days Until Calculator counts down to a future date, and the Business Days Calculator skips weekends and holidays.
What Day of the Week Was That Date?
Every date in history landed on one of seven days: Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, or Saturday. The days repeat in the same order forever, with no breaks. So if you know how many days have passed since some fixed starting point, you can always work out the weekday for any date — past, present, or future.
How the Weekday Is Found
The trick is to turn a date into a single number. Astronomers use the Julian Day Number (JDN), a count of days that starts on January 1, 4713 BCE. Once a date becomes one plain number, you divide by 7 and look at the remainder. Each remainder points to one weekday. Day 0 of this count was a Monday, so a remainder of 0 means Monday, 1 means Tuesday, and so on. If you want to play with remainders on their own, the Modulo Calculator does exactly that step.
Leap Years Change the Pattern
A normal year has 365 days. Since 365 ÷ 7 leaves a remainder of 1, a date usually moves forward one weekday each year. A leap year has 366 days, so it pushes the date forward two weekdays instead. This is why the same date does not follow a simple yearly pattern, and why weekdays repeat in a 28-year loop in the Julian calendar and a 400-year loop in the Gregorian calendar.
- Gregorian rule: a leap year is divisible by 4, but not by 100 — unless it is also divisible by 400. So 2000 was a leap year, but 1900 was not.
- Julian rule: every year divisible by 4 is a leap year, with no exceptions.
Julian vs. Gregorian: Old Style and New Style
The Julian calendar was used across Europe for over 1,500 years. It added a leap day slightly too often, so it drifted away from the seasons by about one day every 128 years. In 1582, Pope Gregory XIII fixed this with the Gregorian calendar we use today.
Countries switched at different times. Britain and its colonies did not change until September 1752, when 11 days were skipped. Dates written before a country switched are called Old Style (O.S.), and dates in the new calendar are called New Style (N.S.). That means one historical event can have two different date labels — and even two different weekdays, depending on which calendar you read it in. Old records often show both, like "February 11/22." To convert a calendar date into the astronomical day count directly, use the Julian Date Calculator.
Split Years (1623/24)
In England before 1752, the new year did not begin on January 1. It began on March 25, called Lady Day. So a date like March 10 was still counted in the old year. To avoid confusion, writers used a double year, such as 1623/24. The first number is the old year start, and the second is the modern one. This only applies to dates from January 1 through March 24.
Why People Look This Up
Knowing the weekday for a date helps with family history and genealogy, checking old letters, diaries, and church records, school and history projects, planning future events, and simple curiosity about the day you were born. For example, July 4, 1776 — the date of the U.S. Declaration of Independence — fell on a Thursday. Genealogists often pair this tool with the Age Difference Calculator or the Days Since Calculator when piecing together a family timeline.
Other Date Facts Worth Knowing
- Day of the year: how many days into the year the date sits, from 1 to 365 (or 366). The Days Calculator handles longer day counts between any two dates.
- ISO week number: a world standard that numbers weeks 1 to 52 or 53, with each week starting on Monday. See the Weeks Calculator for week-based math.
- Season: based on equinoxes and solstices, and flipped for the Southern Hemisphere. The Moon Phase Calculator is a natural companion for sky-watching dates.
- Zodiac sign: the tropical sign tied to the date's place in the solar year. For a deeper reading, try the Birth Chart Calculator, the Chinese Zodiac Calculator, or the Life Path Number Calculator.