Day of the Week Calculator
What day of the week was (or will be) any given date? Useful for historical curiosities and scheduling.
Result
Day of the week
—
How to use this calculator
- Enter a date — past, present, or future.
- Read the day name plus the Zeller's-formula derivation in the steps.
About this calculator
Working out the day of the week for an arbitrary date used to require Zeller's congruence and a bit of mental gymnastics. This calculator gives you the answer immediately and shows the Zeller's steps so you can follow the math by hand for any date in the Gregorian calendar.
Frequently asked
A formula published by German mathematician Christian Zeller in 1882 that computes the day of the week for any date in the Gregorian calendar using only integer arithmetic. It is the standard mental-math approach to "day of the week" puzzles.
Related calculators
Week Number Calculator
Convert any date into its ISO 8601 week number, US week number, and day of the year.
Leap Year Checker
Is a given year a leap year? Apply the Gregorian rule with a step-by-step explanation.
Days Between Dates Calculator
Count the exact number of days between any two dates — all calendar days, weekdays only, or business days (skipping US federal holidays). Pick whether to include both endpoints or just the difference.
Date Add Calculator
Add days, weeks, months, or years to any date and get the resulting date — handles month-end clamping correctly.
Detailed Age Calculator
Calculate age down to the second — years, months, days, hours, minutes, and seconds. Useful for milestones and trivia.
Anniversary Calculator
Years celebrated, days to next, and traditional/modern gift suggestions.