What day of the week is that date?
Enter any date and this calculator answers with its weekday — and, because one fact usually leads to another, it also gives the day of the year, the number of days left in the year, the ISO week number, the quarter, and a table of the whole week around your date. It works for dates centuries in the past or future: the seven-day week has cycled unbroken through all of recorded calendar history, so the answer is a matter of arithmetic, not records.
How the weekday is found
Count the days from any known reference date to yours, take the remainder on division by 7, and step that many places through the week. Computers do this with Julian day numbers; mental mathematicians use the same idea in the Doomsday rule, where memorable dates (4/4, 6/6, 8/8, 10/10, 12/12) all share one weekday per year. Try it: in 2026 those dates are all Saturdays, and this calculator will confirm October 10, 2026 is a Saturday — making October 12 a Monday.
Finding the weekday you were born
The most popular use of this tool: type your birth date and see the day of the week you arrived. Pair it with the Age Calculator for your exact age in days, or the Date Calculator to jump from a known weekday to a future one. Dates before the Gregorian calendar reforms (1582–1923 depending on country) are computed proleptically — the calendar is extended backwards uniformly, which is the standard convention.
The 28-year rule: your old calendar works again
Weekdays advance by one after a common year (365 days is 52 weeks plus 1 day) and by two after a leap year. Over any 28-year stretch inside 1901–2099 there are exactly 7 leap years, so the total shift is a whole number of weeks — and the calendar repeats exactly. Your 1998 calendar is correct again in 2026: both years start on a Thursday, and every date falls on the same weekday.
The cycle breaks at 2100, which is not a leap year despite being divisible by 4 — century years need divisibility by 400. That single missing leap day is why perpetual calendars list corrections for 2100, and why this calculator computes every date from scratch instead of trusting the 28-year shortcut.
Worked example
October 12, 2026 is a Monday — day 285 of 2026, in ISO week 42, with 80 days of the year remaining.
How to use this calculator
- Pick any date — a birthday, a historical date, a future deadline.
- Read the weekday in the green panel.
- Use the stats for day-of-year, ISO week and quarter, and the table below for the surrounding week.
The week that never broke
Calendars have been reformed many times — months renamed, days skipped (October 1582 lost ten days in Catholic countries) — but the seven-day week cycle was never interrupted through any of it. That unbroken chain is exactly why a weekday can be computed for any date with confidence: there is always an unbroken count of sevens back to any reference point you trust.