Weekday of Date
Find the day of the week for any calendar date and follow a step-by-step Doomsday-rule walkthrough in your browser.
Weekday of any date with the Doomsday rule
Need the day of the week for a historical invoice, contract, or trivia question? This tool applies John Conway's Doomsday algorithm: a fixed set of anchor dates per month plus century and year adjustments. You get the weekday name and a numbered walkthrough you can follow on paper.
Why use Doomsday instead of only clicking a calendar?
Calendar widgets answer the question instantly, but the Doomsday rule teaches how weekday arithmetic works modulo 7. It is the same mental model used in competitive calendar challenges and is helpful when you are offline or verifying spreadsheet bugs.
Related: Find Day of Week, Next Weekday Occurrence, and Analyze Calendar Date.
Frequently Asked Questions
Which calendar does the tool use?
Gregorian calendar dates in local form (YYYY-MM-DD). Leap years follow the standard 4/100/400 rules.
What are doomsday dates?
Memorable same-weekday anchors such as 4/4, 6/6, 8/8, and 12/12. January and February use 1/3 or 1/4 and 2/28 or 2/29 on leap years.
Is anything uploaded?
No. Parsing and modulo-7 math run entirely in your browser.
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