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About This Calculator
This calculator reveals what day of the week any date falls on, past or future, using calendar algorithms that account for century rules and leap years. It can determine that July 4, 1776 was a Thursday or find what day your next birthday lands on. Historians, genealogists, and event planners find this tool invaluable for verifying historical records and scheduling around specific weekdays.
Quick Tips
- 1 Use Zeller's formula to mentally calculate the day for any historical date.
- 2 Leap year centuries (2000, 2400) shift weekly patterns by one extra day.
- 3 The Doomsday algorithm lets you find any day of the week in under 10 seconds.
Example Calculation
What day was July 20, 1969 — the Moon landing?
July 20, 1969 was a Sunday | Day 201 of the year | Week 29
How to Determine the Day of the Week
The day of the week for any date can be determined using mathematical algorithms like Zeller's congruence or the Doomsday algorithm. This calculator uses the built-in JavaScript Date engine, which handles all calendar quirks automatically.
Week Numbers Explained
The ISO week number system numbers weeks from 1 to 52 or 53, starting on Monday. Week 1 is the week containing the first Thursday of the year. This system is widely used in business, manufacturing, and international scheduling.
Day of the Year
The day number tells you where a date falls within the year, from 1 (January 1) to 365 or 366 (December 31). This is useful for agriculture, astronomy, and logistics where ordinal dates are standard.
Historical and Future Dates
This calculator works for both historical and future dates. Find out what day of the week you were born, when a holiday will fall next year, or what day a historical event occurred on.
Frequently Asked Questions
Enter your birth date in the calculator to find out. The result will show the exact day name (Monday, Tuesday, etc.) along with additional information about that date.
The calculator uses the ISO 8601 week numbering system. Weeks start on Monday, and the first week of the year is the one containing the first Thursday of January.
Yes. The calculator handles dates across a very wide range. However, keep in mind that the Gregorian calendar was adopted at different times in different countries, so very old dates may not match historical records in some regions.
In the ISO system, if January 1 falls on a Friday, Saturday, or Sunday, it belongs to the last week of the previous year. Week 1 of the new year starts on the following Monday.