Day Of The Week Calculator

Reviewed by the CalculatorHub team, edited by James Graham. Method from CalculatorHub methodology. Last verified 2026-06-23.

The Day Of The Week Calculator computes day of the week from the relation day of week index = (serial day + 4) mod 7 with 0 = Sunday and 6 = Saturday. It takes 3 inputs (year, month 1 to 12, day 1 to 31) and returns the day of the week. These are for anyone working to a fixed calendar or clock: people setting deadlines and milestones, teams and travelers coordinating across regions, administrators counting notice or waiting periods, and anyone planning a personal date or a daily routine, and the result gives you the specific date, time, count or label you can put on a calendar or confirm to someone else. Enter your values below and the result updates instantly, and you can share a permalink that pre-fills the exact calculation. Enter each date or time exactly as it is recorded, note the time zone and stick to a single clock convention (24-hour, or 12-hour with AM and PM) whenever a value carries a time of day, and where a span is involved decide up front whether the start day or start time counts toward the total, since an inclusive versus exclusive endpoint and an unnoticed daylight saving shift are the usual reasons two people get different answers from the same starting point. For example, with year = 2000, month 1 to 12 = 1, day 1 to 31 = 1, the day of the week works out to 6, and the worked example further down the page shows every step so you can follow the arithmetic and reproduce it by hand. The method is the standard form documented by CalculatorHub methodology, and the figure above each result carries the date it was last verified. This is arithmetic over the calendar and clock, so it reports what the dates and times themselves add up to rather than what a particular deadline or routine requires: an employer or institution that counts business days, public holidays and cut-off times by its own rules, a region that shifts its clocks or observes different holidays, and ordinary variation in what a personal schedule has to accommodate can all move the practical answer away from the calculated one.