Day of the Week Calculator
Find out the day of the week for any date in history or the future. Check if you were born on a Monday, or see what day an upcoming holiday falls on.
About the Day of the Week
The Gregorian calendar repeats its cycle every 400 years. Finding the day of the week for any date is a complex calculation involving leap years and century rules.
Zeller's Congruence
Calculators often use an algorithm like Zeller's Congruence to determine the day.h = (q + 13(m+1)/5 + K + K/4 + J/4 - 2J) mod 7
Where q is the day of the month, m is the month (adjusted), K is the year of the century, and J is the zero-based century.
ISO Week Numbers
The ISO 8601 standard defines week numbers. Week 1 is the first week with at least 4 days in the new year. This means if January 1st is a Friday, it counts as part of the last week of the previous year!
? Frequently Asked Questions
This calculator uses the Gregorian calendar logic. Dates before 1582 (when the Gregorian calendar was adopted) might not align historically with the Julian calendar used at the time.
According to international standard ISO 8601, Monday is the first day of the week. However, in the United States and Canada, Sunday is traditionally considered the first day.
Yes. A year is a leap year if it is divisible by 4, except for end-of-century years, which must be divisible by 400.