Date Calculator

Day of Week Calculator

Find what day of the week any past, present, or future date falls on, plus day of the year.

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100% Private: Your calculation happens entirely inside your browser. Your dates are never stored or transmitted.

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What is the Day of Week Calculator?

The Day of the Week Calculator instantly reveals the weekday name for any given calendar date, along with the day number of the year (1–366).

How to Use This Calculator

  1. Select any date (past, present, or future).
  2. Click Calculate to reveal the weekday and additional calendar metrics.

Calculation Logic & Formula

Determined using perpetual calendar mathematics (Zeller’s congruence or Gregorian epoch modular arithmetic).

Worked Example: Day of week for September 16, 2026

Scenario: Finding the weekday for an upcoming international conference.

Calculation: Epoch calculation resolves to Wednesday.

Result: Wednesday (Day 259 of the year, ISO Week 38).

Frequently Asked Questions

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