Day of Week Calculator: Find the Weekday for Any Date in History
Find what day of the week any date falls onโyour birthday, July 4, 1776, or any date. Free instant results. Doomsday Algorithm proof, day name origins, day-of-year stats. Runs locally, no sign-up.
How to Use the Day of Week Calculator
Pick a date in the date picker; the result updates as you type. The main output shows the weekday in large type (e.g., "It's a Tuesday!") with the full long-form date below. A "Did you know?" line rotates facts about that day. "Go to Today" jumps back to the current date. No Calculate or Resetโeverything updates live.
The Doomsday Algorithm: The Math Behind Weekday Calculation
The Doomsday Rule uses modular arithmetic to find the weekday of any date. Each year has a "Doomsday"โa weekday that easy dates (4/4, 6/6, 8/8, 12/12) fall on. The formula combines the century anchor d (e.g., Tuesday for 2000s) with year terms a = โyy/12โ, b = yy mod 12, c = โb/4โ. From there, count forward or back from the nearest doomsday. The Math tab shows the full proof for your selected date.
Day-of-Year and Weekday Occurrence Stats
The result card shows where your date sits in the year: day number out of 365 (or 366), days left in the year, and which occurrence of that weekday it is (e.g., the 7th Tuesday of 52). Useful for project milestones, countdowns, and calendar trivia.
Why Tuesday, Wednesday, Thursday? The Origins of Day Names
Most English day names come from the seven "wandering stars" visible in antiquityโthe Sun, Moon, and five planets. Sunday and Monday are straightforward. Tuesday through Friday honor Norse gods (Tiw, Woden, Thor, Frigg), mirroring Roman gods (Mars, Mercury, Jupiter, Venus). Saturday kept its Roman nameโSaturn's day. "Thursday" nods to Thor; "Wednesday" to Woden (Odin). The Day Trivia tab goes deeper.
Day of Week Calculator FAQ
? How do I find the day of the week for any date?
Pick any date in the date pickerโthe result updates live. You'll see the weekday (e.g., "It's a Tuesday!") and full date. "Go to Today" resets to the current date.
? What is the Doomsday Algorithm?
The Doomsday Rule finds weekdays using modular arithmetic. Each year has a "Doomsday"โa weekday that 4/4, 6/6, 8/8, and 12/12 fall on. The formula uses the century anchor d and year terms a, b, c. The Math tab shows the step-by-step proof for your date.
? Where do Tuesday, Wednesday, Thursday get their names?
Most English day names blend Roman and Norse mythology. Sunday and Monday come from the Sun and Moon. Tuesday through Friday honor Norse gods (Tiw, Woden, Thor, Frigg), mirroring Roman gods (Mars, Mercury, Jupiter, Venus). Saturday kept its Roman nameโSaturn's day.