Day of the Week Calculator
Pick any date and see the day of the week it fell on — or will fall on. It answers the classic 'what day was I born on?' (and whether your birthday lands on a weekend next year), plus historical curiosity: moon landings, royal weddings, and that concert you remember being at.
Alongside the weekday you get the day-of-year number and the ISO week number, which is the detail project plans and European calendars quietly rely on.
How to use
- Pick any date — past or future — from the date picker.
- Read the weekday instantly, plus the day-of-year and ISO week number.
- Change the year to plan birthdays: see whether yours falls on a weekend next time.
Frequently asked questions
What day of the week was I born?
Enter your date of birth and the weekday appears instantly. The pattern repeats every 28 years (the solar cycle), so your birth date falls on the same weekday as it did 28 years ago.
Does the calculator work for any year in history?
It uses your browser's proleptic Gregorian calendar, accurate across a huge historical range. For dates before 1582 (when the Gregorian calendar was introduced) historians use the Julian calendar, so results may differ from historical records.
Why do dates fall on different weekdays each year?
A year is 365 days — one day longer than 52 weeks — so each year's dates shift one weekday later (two after a leap year). That is why your birthday keeps moving.
What is the ISO week number?
A standard way of numbering weeks (1–52/53) used in European business calendars: week 1 is the week containing the first Thursday of January.