Find the weekday, day of year and ISO week for any date.
Calculated locally in your browser.
How do you find what day of the week a date falls on?
The weekday is derived directly from the calendar date, and you also see the day of the year (counting from 1 on 1 January), the ISO week number and whether it's a leap year. ISO week 1 is the week containing the first Thursday of the year. For example, 22 June 2026 falls on a Monday — day 173, ISO week 26.
Understanding your result
The day of year counts from 1 on 1 January; leap years have 366 days.
Formula and method
The weekday is derived from the calendar date. ISO week 1 is the week containing the first Thursday of the year.
Assumptions and limitations
Results follow the proleptic Gregorian calendar, so historical dates from before its adoption in a given country may not match the calendar actually used then. The tool reports calendar facts for a date only and does not account for time zones or the time of day, which do not affect the weekday.
Worked example
22 June 2026 falls on a Monday — day 173 of the year, ISO week 26.
How to use this tool
- Pick a date.
- Read the weekday and extra details.
Common mistakes to avoid
- Confusing ISO week numbering with simple “week of the month”.
About the Day of the Week
Find out what day of the week any date falls on, along with the day of the year and ISO week number.
Who should use this tool
Anyone checking the weekday of a birthday, deadline or historical date.
Benefits
- Reveals the weekday for any past or future date instantly.
- Shows the day-of-year number, counting from 1 on 1 January.
- Gives the ISO week number based on the first Thursday rule.
- Handles leap years automatically so 366-day years are counted correctly.
Practical use cases
- Finding which weekday a historical event fell on.
- Checking the weekday of a future deadline or appointment.
- Looking up the ISO week number for scheduling or reporting.
- Settling a bet about what day someone was born on.
Explore all Date and Time tools
Frequently asked questions
What is an ISO week?
A standard week numbering where week 1 contains the year’s first Thursday and weeks start on Monday.
Does it handle leap years?
Yes. The day-of-year total shows 366 in leap years.
Does the time of day change the weekday?
No. A weekday is a property of the calendar date itself, so the hour and minute make no difference. Whatever time you check, a given date always falls on the same day of the week, and the day-of-year and ISO week values are unchanged too.