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Date & TimeFormula-based · Runs in your browser

Day of Week Calculator

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

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Inputs

Enter the values you know. Optional fields may be left empty.

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Required

Result

Updates as valid inputs change.

Calculated locally
Weekday
—
Day of year
—
ISO week
—
Leap year
—

Saved locally, explained clearly

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Calculation steps

Follow what happened from the selected formula to the displayed answer.

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  1. 1

    Formula selected

    The calculator uses the following formula or method.

    Weekday and ISO week are derived from the Gregorian calendar date

  2. 2

    Values entered

    Your values are placed into the calculation.

    Enter values to see what is used in this step.

  3. 3

    Result calculated

    The formula or method produces the following result values.

    Results will appear after a successful calculation.

  4. 4

    Answer formatted

    Displayed values are rounded and formatted using each output’s configured precision.

Scenario comparison

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Recent calculations

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Data and privacy

How it works

The date is parsed without a local time zone. ISO weeks begin on Monday and week 1 contains the year’s first Thursday.

Input query strings and outputs

Use an input name in this page’s URL as ?name=value, and join additional inputs with &. Portable shared links may instead use the compact ?ac= state parameter.

Input query strings

1
  • ?date= Date

    Date · Required · Default: 2026-08-18

Outputs

4
  • weekday Weekday

    Text · Primary output

  • dayOfYear Day of year

    Whole number

  • isoWeek ISO week

    Whole number

  • leapYear Leap year

    Text

Sources
  • No external reference is listed for this calculator. Its formula and variable definitions are shown above.
Limitations
  • Calendar results depend on the selected dates and time-zone assumptions. Local holidays and daylight-saving changes are included only where stated.

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