Apr 30, 2026
- ISO weekday
- 4
- Sunday-based index
- 4
- Date
- 2026-04-30
Day of the Week Calculator
Use this free day of the week calculator to find whether a date falls on Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, or Sunday.
Inputs explainedResult checksExample valuesRuns in your browser
Formula steps
- Read the entered date as a calendar date.
- Use UTC date math so daylight-saving time does not shift the date.
- Return both the weekday name and ISO weekday number.
Examples
Recent answers
Recent day-of-week checks will appear here.
Date checks use UTC calendar dates in this browser tab.
Inputs and recent answers stay in this browser tab and are not sent to a server.
How to use the Day of the Week Calculator
- Choose a calendar date.
- Press Find day of week to see the weekday name and ISO weekday number.
- Use Date Calculator instead when you need days between dates.
- Check time zones separately for events that happen near midnight.
What people use it for
Find the weekday for a birthday, deadline, holiday, or event date.
Check ISO weekday numbers for scheduling notes.
Compare leap-day and future date examples.
Use date-only math without time-of-day confusion.
Quick examples
Today
2026-04-30Thursday
New Year 2027
2027-01-01Friday
Leap day
2024-02-29Thursday
Need the guide or a nearby tool?
Need a slower walkthrough, a related calculator, or the full library? These links keep you close to the task you started.
- How to use the Day of the Week CalculatorSee slower examples, input meanings, formula notes, result limits, and mistakes to avoid.
- Date & TimeBrowse related calculators and utilities in the same category.
- Calculator and utility guidesFind more guides that use real tool inputs and example numbers.
- All free toolsSearch every live tool, converter, calculator, AI helper, and browser utility.
Frequently asked questions
Plain-language answers about when to use the tool, what it does with your inputs, what to double-check, and how privacy works.
When should I use the 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 one valid calendar date with the exact year, month, and day you want to check.
What is the Day of the Week Calculator doing with my inputs?
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 date example before copying the answer.
What do the main Day of the Week Calculator inputs mean?
Date: the calendar date you want to turn into a weekday name and weekday number.
How should I read the Day of the Week Calculator answer?
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.
What should I double-check before trusting the answer?
This uses calendar-date math only. Historical calendars, local calendar reforms, and time-zone-specific date changes can require specialized references. Also double-check the exact year, month, day, local time-zone edge cases near midnight, and whether an old historical record used a different calendar.
Why does the calculator use UTC date math?
It treats the entry as a calendar date, not a clock time. UTC date math keeps daylight-saving changes or your local browser time zone from shifting the date to the day before or after.
What is the difference between ISO weekday and Sunday-based index?
ISO weekday numbers Monday as 1 through Sunday as 7. The Sunday-based index numbers Sunday as 0 through Saturday as 6, which matches many programming date APIs.
Can I use this for very old historical dates?
Use caution. The tool uses modern calendar-date math, but older records may follow different local calendars or calendar-reform dates. Historical research can need a specialized calendar source.
Does the site save what I enter?
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.