# Day of Week Calculator

> Find the weekday, day of year, ISO week number, and leap-year status.

Page: https://askcalculators.com/calculator/day-of-week-calculator/
Definition: https://askcalculators.com/calculator/day-of-week-calculator/definition.json
JSON Schema: https://askcalculators.com/calculator/day-of-week-calculator/schema.json
Version: 1.0.0
Maintained by: AskCalculators (software project; not a credentialed reviewer)
Qualified review: pending. Automated checks do not establish professional approval.
Page status: Live
Review status: Pending

## Use
Open the calculator page and enter values. Query-string parameters can restore and bookmark a calculation.
Example: https://askcalculators.com/calculator/day-of-week-calculator/?date=2026-08-18

## Inputs
- date: Date; type=date; required; default=2026-08-18

## Outputs
- weekday: Weekday; format=text; primary
- dayOfYear: Day of year; format=integer
- isoWeek: ISO week; format=integer
- leapYear: Leap year; format=text

## Formula
Weekday and ISO week are derived from the Gregorian calendar date

## Rules
- Empty optional inputs are undefined, not zero.
- Hidden conditional inputs are ignored.
- Do not invent missing required inputs.