Find out what day of the week any date falls on. Perfect for historical dates, birthdays, or planning future events.
Last updated: March 2026
The seven-day week is one of humanity's oldest continuous time-keeping systems, with roots in ancient Babylonian astronomy. Babylonians observed seven celestial bodies visible to the naked eye: Sun, Moon, Mars, Mercury, Jupiter, Venus, and Saturn. Each was assigned a day, creating the seven-day cycle that persists today across nearly all cultures.
English day names blend Latin and Germanic mythology. Sunday and Monday retain their Roman origins (Sun and Moon). Tuesday through Friday honor Germanic gods (Tiw, Woden, Thor, Frigg) who were matched to Roman deities (Mars, Mercury, Jupiter, Venus). Saturday alone preserves its direct Roman name (Saturn's Day). This linguistic fusion reflects England's history: Celtic foundations, Roman occupation, then Germanic (Anglo-Saxon) settlement.
Knowing historical days of the week satisfies curiosity ("What day was I born?") and has practical uses. Historians verify event dates, genealogists research family records, and planners determine optimal days for events. The calculation involves complex modular arithmetic (like Zeller's congruence), accounting for leap years and Gregorian calendar reforms—calculations this tool performs instantly.
JavaScript's Date object uses a sophisticated algorithm that accounts for:
What day was the U.S. Declaration of Independence signed?
Computer systems often use 0-based indexing. JavaScript follows this convention with Sunday=0. Some international standards (ISO 8601) use Monday=1, but the calculator shows both the name and number for clarity.
Yes, but with caveats. The Gregorian calendar was adopted in 1582 (varying by country). Dates before this used the Julian calendar. The calculator assumes Gregorian rules for all dates, so pre-1582 results may differ from historical records.
The calculator works for dates far into the future (JavaScript supports years up to 275,760). However, if calendar systems change in the future, the day name might become historical rather than actual.
Different languages preserve different mythological traditions. Romance languages (Spanish, French) use Roman gods. Slavic languages often use numbers. Chinese uses elements. But the seven-day cycle is nearly universal.
Absolutely! Enter your birth date to see what day you were born. This is a popular use case—many people find it interesting to know if they were born on a Monday, Friday, etc.
Historians verify event dates (records sometimes conflict on dates but agree on day-of-week). Genealogists cross-reference family records. Event planners avoid scheduling on the same day-of-week as past failed events.
Germanic peoples matched their gods to Roman weekday gods. Roman Thursday was Jupiter's Day (Jovis Dies). Germans equated Jupiter with Thor (both thunder gods), creating Thor's Day → Thursday.
Nearly all modern cultures do, though not historically. Ancient Egyptians used 10-day weeks, Romans used 8-day markets. The 7-day week spread globally through Roman and later religious (Jewish, Christian, Islamic) influence.
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