Calculatorism

Day of the Week Calculator

Enter any date to instantly see its weekday (English/Chinese) and ISO weekday number (Mon=1 … Sun=7).

Input Data

The date to look up (YYYY-MM-DD).

Results

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At a glance:The day of the week calculator finds the weekday of the entered date and expresses it with ISO-8601 numbering: Monday = 1, Sunday = 7.

Formula

jsDay = date.getDay() (0=Sun … 6=Sat).

dayNumber = (jsDay + 6) mod 7 + 1 (Mon=1 … Sun=7).

Weekday name maps from dayNumber in the chosen language.

How to Use

  1. Enter the date to look up.
  2. See the weekday name and ISO number instantly.

FAQ

What is the ISO weekday number?

ISO-8601 treats Monday as the first day of the week, numbered 1–7. Many scheduling and accounting systems use this numbering to compute 'day of week'.

Does English mode show the English weekday?

Yes. On the English page the weekday name is shown in English (Monday … Sunday), localized alongside the result.

Related Tools

References

Content reviewed by the Calculatorism editorial team. Results are for reference only; please refer to the relevant authorities for the official figures.

Found a problem with the results?

If this calculator's result is wrong, or you have any question about the calculation logic, please let us know. You are viewing:Day of the Week Calculator（/everyday-life/day-of-the-week）。