Find out what day of the week any past or future date falls on, with day-of-year numbers and historical facts.
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A day of the week calculator determines the specific weekday (Sunday through Saturday) for any date in past or future history. It uses modular calendar mathematics (such as Zeller’s Congruence or the Doomsday rule) to instantly find the weekday for any event.
h = \left( q + \left\lfloor \frac{13(m+1)}{5} \right\rfloor + K + \left\lfloor \frac{K}{4} \right\rfloor + \left\lfloor \frac{J}{4} \right\rfloor - 2J \right) \pmod{7}Where q is day of month, m is shifted month, K is year of century, and J is zero-based century.
Scenario: What day of the week was the Apollo 11 Moon landing on July 20, 1969?
Date: July 20, 1969.
Apply calendar modulo math.
July 20, 1969 was Day #201 of the year 1969.
January 1, 2000 was a Saturday.
It calculates using the standard Gregorian calendar algorithm, factoring in leap years and century rules.
The Doomsday rule is a mental math algorithm created by mathematician John Conway that allows someone to quickly calculate the day of the week for any date.
Yes, the calendar repeats in cycles of 6, 11, 11, and 28 years, and repeats identically every 400 years.
Add or subtract days, weeks, months, and years from any date or calculate the exact duration between two dates.
Calculate exact age in years, months, and days, countdown to next birthday, generation name, and total days lived.
Check if any year is a leap year, explore next and past leap years, and understand the Gregorian 400-year rule.
Weekend day
#201
out of 365/3661969
CE