// discover the weekday for any past or future date
Find the exact weekday for any birthday or date — past or future. Discover if you were born on a Monday, Friday, or any day of the week instantly.
Pick a date to discover its weekday
Enter any birthday, anniversary, or historical dateUse the date picker or type a date directly into the input field.
Hit the button — or use Ctrl+Enter — to instantly calculate the day of week.
See the weekday, day of year, week number, zodiac sign, and fun trivia.
This tool uses the Zeller's congruence algorithm to calculate the exact weekday for any date in history or the future. Simply pick a date and discover if it falls on a Monday, Friday, or any day of the week.
Enter your full birth date (day, month, year) into the date picker and click "Find Day." The tool instantly calculates the exact weekday you were born on — Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, or Sunday.
The tool supports any date from year 0100 to 9999, covering thousands of years of history. Whether you want to know what day Julius Caesar was assassinated or what weekday a future date falls on, this tool handles it.
Yes, the algorithm accounts for the Gregorian calendar reform. Dates before October 15, 1582 are handled using the proleptic Gregorian calendar, which is the standard approach for historical date calculations.
This tells you how many days separate the selected date from today. A negative number means the date is in the past; a positive number means it's in the future. This is useful for planning or understanding how long ago an event occurred.
The tool uses ISO 8601 week numbering, where weeks start on Monday and the first week of the year is the one containing the first Thursday. This is the standard used in most European countries and international business contexts.
Absolutely! The day-of-week calculation works equally well for past and future dates. Use it to plan events, check what day a holiday falls on in future years, or find the weekday for a far-future date.
One of the most common and fun questions people ask is: "What day of the week was I born?" Whether you're curious about your own birth date, want to find out what weekday a historical event occurred on, or need to know what day of the week a future date falls on, our Birthday Day of Week Finder gives you an instant, accurate answer.
Simply enter any date — from ancient history to the far future — and the tool immediately calculates the exact weekday. You'll also see the day of the year, ISO week number, how many days away the date is from today, and even the zodiac sign associated with that date.
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The algorithm behind this tool is based on a deterministic mathematical formula that maps any calendar date to a day of the week. The most well-known version of this is Zeller's congruence, developed by German mathematician Christian Zeller in the 19th century.
The formula takes into account the day, month, year, and century, then applies modular arithmetic to produce a number from 0 to 6 representing the weekday. Our implementation uses JavaScript's built-in Date object for modern dates, which handles all edge cases including leap years automatically.
The Gregorian calendar — the one used worldwide today — was introduced by Pope Gregory XIII in October 1582 to correct drift in the older Julian calendar. The key rule for leap years in the Gregorian system:
So 1900 was not a leap year, but 2000 was. This 400-year cycle means the Gregorian calendar repeats exactly — meaning January 1, 2000 was a Saturday, and so will January 1, 2400 be.
Did you know that the 13th of any month is more likely to be a Friday than any other day of the week? It's true — over the full 400-year Gregorian cycle, Friday the 13th occurs 688 times, more than any other day-date combination. Here are more interesting facts:
Many famous figures in history were born on notable days of the week. Albert Einstein was born on a Friday (March 14, 1879). Marilyn Monroe was born on a Tuesday (June 1, 1926). Barack Obama was born on a Friday (August 4, 1961). Using this tool, you can discover the exact weekday for any birth date in recorded history.
The ISO 8601 standard defines week numbering in a specific way that's used internationally, especially in business and project management. Key rules:
This means that dates at the very end of December might technically belong to "Week 1" of the following year, and similarly, early January dates could be in "Week 52" or "Week 53" of the previous year.
Along with the weekday, our tool also shows you the Western zodiac sign for any date. The 12 signs of the Western zodiac are based on the position of the Sun relative to star constellations at the time of birth:
Beyond finding your birth weekday, this tool is incredibly useful for planning. Want to know if New Year's Day will fall on a Monday in 2030? Wondering what day your company's anniversary will land on five years from now? Need to know what weekday Christmas falls on this year? Just enter the date and get an instant answer.
Event planners, project managers, teachers, and anyone who works with calendars will find this tool helpful for quickly determining the weekday of any date without needing to open a calendar application.
History enthusiasts can use this tool to verify dates in historical records. What day of the week did World War II end? What weekday was the moon landing? What day did the Berlin Wall fall? Enter any date and find out instantly. This is particularly useful for historians, writers, and researchers who need to cross-reference dates with weekdays for accuracy.