Week, Month & Year Tools
Day of the Week Calculator
Find the exact day of the week for any date in history or the future.
Day of the Week
Sunday
July 20, 1969
Day 201
Day of Year
365 Days
Days in Year
About the Day of the Week Calculator
What day of the week were you born on? What day of the week was the Apollo 11 Moon Landing? The Day of the Week Calculator determines the weekday for any calendar date using Zeller’s congruence algorithm.
How to Use This Calculator
- Enter any Date.
- Click Find Weekday.
- Discover the day of the week, day of the year (1-366), and astrological sign.
Calculation Method & Mathematical Formula
Based on Zeller’s Congruence for the Gregorian calendar:
h = (q + [13(m+1)/5] + K + [K/4] + [J/4] - 2J) mod 7
Worked Example
Scenario: July 20, 1969 (Moon Landing):
- Day of Week: Sunday.
- Day of Year: Day 201 of 365.
- Zodiac Sign: Cancer.
Important Calendar Notes
Zeller’s formula treats January and February as months 13 and 14 of the previous calendar year.
Frequently Asked Questions
Related Calculators
Last reviewed by editorial team on September 13, 2026
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Disclaimer: Applicable to the standard Gregorian calendar.