Day of Week Calculator

Which weekday any date falls on — past or future.

Day of Week Calculator

Worked example result

Day of the week	Saturday
Day number (Mon=1 … Sun=7)	6
Is it a weekend?	Yes

March 14, 2026 falls on a Saturday — day number 6, and a weekend day.

Enter any date to learn the day of the week it falls on, its weekday number in the Monday-first convention (Monday = 1 to Sunday = 7), and whether it is a weekend day.

Works for historical dates and far-future dates alike, using exact calendar arithmetic rather than lookup tables.

The formula

Weekday read from the date's position in the 7-day cycle (UTC calendar arithmetic); Day number = Mon 1 … Sun 7

Worked example

March 14, 2026 falls on a Saturday — day number 6, and a weekend day.

The example is pre-loaded in the result panel — press Calculate with your own numbers to replace it.

Frequently asked questions

What day of the week was I born on?

Enter your birth date exactly as it appears on your birth certificate and the calculator returns the weekday instantly.

Why does the day number start on Monday?

The Monday = 1 … Sunday = 7 numbering is the ISO 8601 convention used by most of the world and by business calendars. Sunday-first numbering is common only in US-style calendars.

Category: Date & Time calculators

Day of Week Calculator