Day of the Week Calculator

Use it when your task matches one of these common needs: Find the weekday for a birthday, deadline, holiday, or event date. Check ISO weekday numbers for scheduling notes. It works best when you already know the measurements, amounts, units, or options the page asks for.

In plain language: The calculator reads the date as a UTC calendar date and returns the weekday name, Sunday-based index, and ISO weekday number. The examples on the page are there so you can compare your inputs with a worked example before copying the answer.

The main inputs are the measurements, amounts, units, or options the tool needs before it can work. Read each field label, keep units consistent, and compare your entry with the examples if the answer looks strange.

Read the headline answer, then check the supporting lines and examples to understand how the calculator got there. If one input changes, rerun the tool and compare the new answer instead of guessing.

This uses calendar-date math only. Historical calendars, local calendar reforms, and time-zone-specific date changes can require specialized references. Also check the unit, scale, mode, and result limit because small input changes can change the answer.

No. The calculator runs in your browser tab. Your recent answers stay only on the page while you use it, and they are not sent to a server.