Day of the Week Calculator

Choose a date to see the day of the week.

Day of the Week Calculator Online – Calculate Dates Easily

Intro

Ever wondered what day of the week you were born? Or which weekday a future event falls on? Manually figuring it out can be confusing, especially when leap years and calendar changes are involved. That’s why the Day of the Week Calculator online is so useful.

This free tool instantly tells you the exact weekday for any date—past, present, or future. Whether you’re planning an event, checking a birthday, or just curious about history, this calculator makes it quick and accurate.

Formula / Working

The day of the week is calculated using algorithms like Zeller’s Congruence or the Doomsday Rule. These formulas convert a given date into a number representing the weekday.

Zeller’s Congruence Formula:

h=(q+13(m+1)5+K+K4+J4+5J)mod 7h = \left(q + \frac{13(m+1)}{5} + K + \frac{K}{4} + \frac{J}{4} + 5J \right) \mod 7h=(q+513(m+1)+K+4K+4J+5J)mod7

Where:

h = Day of the week (0 = Saturday, 1 = Sunday, …, 6 = Friday)
q = Day of the month
m = Month (March = 3, …, January and February are counted as months 13 and 14 of the previous year)
K = Year of the century (year % 100)
J = Zero-based century (year / 100)

The calculator applies this automatically, so you don’t need to do the math yourself.

Step-by-Step Usage

Here’s how to use the Day of the Week Calculator online:

Enter the date (day, month, and year).
Click on the “Calculate” button.
Instantly see the exact day of the week.

It works for any valid date in history or the future.

Examples

Example 1

Input: July 20, 1969 (Apollo 11 Moon Landing)
Result: Sunday

Example 2

Input: January 1, 2000
Result: Saturday

Example 3

Input: September 11, 2025
Result: Thursday

FAQs

1. What is a Day of the Week Calculator?
It’s a tool that tells you which weekday corresponds to any given date.

2. Can it calculate past historical dates?
Yes, it works for both historical and future dates, as long as the Gregorian calendar applies.

3. How accurate is this calculator?
It uses precise calendar formulas, ensuring 100% accuracy for valid dates.

4. Do leap years affect the calculation?
Yes, but the algorithm automatically accounts for leap years, so you don’t need to worry.

5. Why would I need this tool?
It’s useful for event planning, astrology, genealogy research, or simply satisfying curiosity about birthdays and anniversaries.