Results use the proleptic Gregorian calendar. Historical places adopted the Gregorian calendar on different dates, so very old civil records may use another calendar.
How to use this day of the week calculator
- Choose a past, present or future date.
- Select Calculate.
- See the weekday, day of year, ISO week and distance from today.
Find the weekday for any date
Enter one valid calendar date and the calculator returns its weekday, the full date, its numbered day within the year, its ISO week and whether it falls on a working weekday or weekend. It also shows how many calendar days the date is before or after today. This is useful for checking a birth date, anniversary, deadline, historical event or future booking without paging through a calendar.
How the day of the week is calculated
The selected date is validated and handled as a date-only UTC value. That keeps daylight-saving clock changes and your device time zone from shifting the answer to the previous or next day. The browser then applies the Gregorian calendar's repeating seven-day cycle. Leap years and real month lengths are included automatically, including 29 February when the year is divisible by four except most century years; century years divisible by 400 remain leap years.
Day number and ISO week number
Day of year counts 1 January as day 1. In a leap year, 31 December is day 366; otherwise it is day 365. ISO week numbers run Monday through Sunday. ISO week 1 is the week containing the year's first Thursday, so dates near New Year's Day can belong to the previous or next ISO week-numbering year. The result shows both the ISO week and its week-numbering year to make that edge case clear.
Worked examples
1 January 2000 was a Saturday, day 1 of the year and part of ISO week 52 of 1999. Leap day, 29 February 2024, was a Thursday and day 60 of 2024. These fixed examples are covered by automated tests so leap years and week-year boundaries cannot silently change.
Historical calendar note
This tool extends today's Gregorian calendar rules backward for consistent calculation. Countries adopted that calendar at different times, and older records may use the Julian calendar or omit dates during a local changeover. For historical research, check which civil calendar the original record used.
Choose the right date tool
Use Age Calculator for an exact age, Days Between Dates for the gap between two dates, or Add or Subtract Days to move forward or backward from a starting date.
Frequently asked questions
Can I check a future date?
Yes. The same calendar rules work for valid past and future dates supported by your browser.
Does my time zone change the weekday?
No. The input is treated as a calendar date rather than a moment in time, so time-zone offsets do not shift it.
Is Saturday a weekday?
No. This result labels Monday through Friday as weekdays and Saturday and Sunday as weekends.