How to Calculate Day of the Week
What is Day of the Week?
A day-of-week calculator determines what day of the week any given date falls on. The Doomsday algorithm (Conway) or modular arithmetic can compute this for any date in the Gregorian calendar.
Step-by-Step Guide
- 1Use the formula: (d + m + y + y/4 − y/100 + y/400 + c) mod 7
- 2d=day, m=month code, y=year, c=century adjustment
- 3Or simply count forward/backward from a known reference date
- 4JavaScript: new Date("YYYY-MM-DD").getDay() → 0=Sunday, 6=Saturday
Worked Examples
Input
July 4, 1776
Result
Thursday
US Independence Day
Input
January 1, 2000
Result
Saturday
Y2K millennium
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