Find out what day of the week any past or future date falls on. Includes week number, day of the year, and zodiac sign.
The Gregorian calendar (the one most of the world uses today) has a fixed pattern: 365 days in a normal year, 366 in a leap year. Because 365 ÷ 7 = 52 remainder 1, each calendar date shifts by one day of the week each year (or two days across a leap year). The calculator uses JavaScript's built-in date math, which is accurate from year 1 to year 275,760.
ISO 8601 defines week 1 as the week containing the first Thursday of the year. Weeks always start on Monday. This means January 1st might be in week 52 or 53 of the previous year if it falls on Friday, Saturday, or Sunday. Most European countries and international standards use ISO weeks. The US often uses a different convention where week 1 starts January 1st.
| Event | Date | Day |
|---|---|---|
| Declaration of Independence signed | July 4, 1776 | Thursday |
| Wright brothers first flight | December 17, 1903 | Thursday |
| End of WWII (V-J Day) | September 2, 1945 | Sunday |
| Apollo 11 moon landing | July 20, 1969 | Sunday |
| Berlin Wall fell | November 9, 1989 | Thursday |
| Y2K (start of 2000) | January 1, 2000 | Saturday |
| 9/11 attacks | September 11, 2001 | Tuesday |
| iPhone launch | June 29, 2007 | Friday |
| COVID-19 pandemic declared | March 11, 2020 | Wednesday |
The mathematician John Conway invented a mental algorithm to find the day of the week for any date. It uses "doomsdays" — specific dates that always fall on the same day of the week within a given year. For example, in 2026 the doomsday is Saturday. Knowing the doomsdays for each month (4/4, 6/6, 8/8, 10/10, 12/12, the last day of February) lets you calculate any date with practice.