Day of Week Calculator

Calculator

Calendar

Historical

Formula

FAQ

Enter any date to find out what day of the week it was, is, or will be.

Select Date

Or Enter Manually

Interactive Calendar

Click on any date in the calendar to see what day of the week it falls on.

Historical Events

Important historical dates and what day of the week they occurred on.

Major Historical Events

July 4, 1776

Thursday

American Independence

The Declaration of Independence was signed

July 20, 1969

Sunday

Moon Landing

Neil Armstrong first walked on the moon

Nov 9, 1989

Thursday

Berlin Wall Falls

The fall of the Berlin Wall began

Sep 11, 2001

Tuesday

9/11 Attacks

Terrorist attacks on World Trade Center

Jan 1, 2000

Saturday

Y2K Millennium

The new millennium began

Historical Date Examples

Date	Day of Week	Event	Significance
Dec 7, 1941	Sunday	Pearl Harbor Attack	US enters WWII
Aug 15, 1969	Friday	Woodstock Begins	Cultural milestone
Nov 22, 1963	Friday	JFK Assassination	National tragedy
Oct 29, 1929	Tuesday	Black Tuesday	Stock market crash
Apr 14, 1865	Friday	Lincoln Shot	Good Friday assassination
Dec 25, 1	Saturday	Christmas Day	Traditional birth of Christ

Mathematical Formula

The mathematical algorithm used to calculate the day of the week for any date.

Zeller's Congruence Formula

Adjust the month and year (January and February are counted as months 13 and 14 of the previous year)

Calculate: h = (q + ⌊13(m+1)/5⌋ + K + ⌊K/4⌋ + ⌊J/4⌋ - 2J) mod 7

Where: q = day, m = month, K = year % 100, J = year / 100

Result: h = 0 (Saturday), 1 (Sunday), 2 (Monday), ..., 6 (Friday)

Alternative Methods:

Doomsday Algorithm: Developed by John Conway, uses anchor days
Key Value Method: Assigns values to months and centuries
Gauss Formula: Another mathematical approach by Carl Gauss
Mental Calculation: Various shortcuts for quick mental math

Manual Calculation Example

Step	Calculation	Value	Description
1	Date	July 16, 2025	Original date
2	q (day)	16	Day of month
3	m (month)	7 (July)	Month number
4	K (year mod 100)	25	Last two digits of year
5	J (year div 100)	20	First two digits of year
6	Formula result	4	Wednesday (day 4)

Frequently Asked Questions

How accurate is this calculator? The calculator is accurate for all dates in the Gregorian calendar (from 1582 onwards) and Julian calendar dates before that.
What about dates before 1582? Dates before the Gregorian calendar reform use the Julian calendar system. The calculator automatically handles this transition.
Why do some historical sources differ? Different regions adopted the Gregorian calendar at different times. Some countries didn't switch until the 18th-20th centuries.
Can I calculate future dates? Yes, the calculator works for any future date, assuming the current calendar system continues to be used.
What about leap years? The calculator automatically accounts for leap years in both Julian and Gregorian calendar systems.
How do I verify the results? You can cross-reference with historical records, other date calculators, or use the mathematical formulas provided.
What's the earliest date I can calculate? Theoretically any date, but historical accuracy decreases for very ancient dates due to calendar system changes.
Why do weekdays repeat every 400 years? The Gregorian calendar repeats exactly every 400 years (146,097 days = 20,871 weeks exactly).

📅 Day of Week Calculator