What Is a Day of the Week Calculator?
A day of the week calculator tells you which day — Monday through Sunday — any date falls on. Pick a past, present, or future date and the weekday name appears instantly, along with extra details like the ISO day number, week number, and a visual month calendar.
It is handy for anyone who needs to know the weekday behind a date: planners checking whether an event lands on a weekday or weekend, researchers dating historical events, and the simply curious who want to know what day they were born on.
How to Use the Weekday Calculator
Pick a date
The tool opens on today's date with the weekday already shown. Click the Select Date picker to choose another date, or press Today to jump back to the current day.
Read the result
The day name appears in large text (for example, "Friday") with the full formatted date below it, plus a Weekday or Weekend badge and the ISO day number.
Explore date details
The details card shows the day of year, ISO week number, calendar quarter, days in the month, leap year status, and days remaining in the year.
Use the month calendar
A visual calendar highlights the selected date and today. Click any other day to instantly switch to it, then press Copy Result to save the date and day to your clipboard.
Features
Instant Day Identification
Select any date and immediately see the day of the week in large, bold text you can read at a glance.
Weekday and Weekend Detection
A color-coded badge shows whether the date is a weekday (Monday to Friday) or a weekend (Saturday or Sunday).
ISO Day Number
The ISO 8601 day number appears beside the day name — Monday is 1, Sunday is 7 — for software, APIs, and spreadsheets.
Comprehensive Date Details
See the day of year, ISO week number, quarter, days in the month, leap year status, and days remaining in the year.
Interactive Month Calendar
A visual month calendar highlights the selected date and today; click any day to check its weekday in one tap.
Works for Any Date
Check dates in the past, present, or future — from historical events to dates years from now — with accurate results.
Frequently Asked Questions
What day of the week was I born?
Enter your date of birth in the date picker and the day of the week appears instantly. Many people are curious whether they were born on a Monday, a Friday, or any other day.
How do I find the day of the week for any date?
Open the date picker, choose the date you want, and the weekday name appears with the full formatted date. You can also click a day in the month calendar below to switch to it without reopening the picker.
What does the ISO day number mean?
ISO 8601 assigns each weekday a number: Monday = 1, Tuesday = 2, Wednesday = 3, Thursday = 4, Friday = 5, Saturday = 6, Sunday = 7. This numbering is used in programming, databases, and international business.
Why does the week start on Monday?
The ISO 8601 international standard defines Monday as the first day of the week, which is the convention in most of Europe and in software systems. In the United States, Sunday is traditionally counted first, even though ISO numbering begins with Monday.
How far back and forward can I check dates?
The calculator uses your browser's built-in date engine, which handles a very wide range of dates. You can check days centuries in the past — such as a famous historical event — or far into the future.
Is my data private?
Yes. Every calculation runs entirely in your browser and no date is sent to any server. Your last selection is stored locally on your device so it is ready when you return.
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