Enter a date and the calculator tells you its weekday, where it sits in the year, its ISO week number and whether the year is a leap year. It also lists the next years in which the same date falls on the same weekday – useful for reusing an old calendar or planning an anniversary.
Example: December 25, 2026 is a Friday: day 359 of 365, in ISO week 52, in the fourth quarter. The next years with Christmas on a Friday are 2037, 2043 and 2048.
Famous dates
| Date | Weekday |
|---|---|
| November 22, 1963 | Friday |
| July 20, 1969 (Moon landing) | Sunday |
| November 9, 1989 (fall of the Berlin Wall) | Thursday |
| January 1, 2000 | Saturday |
| September 11, 2001 | Tuesday |
| May 8, 1945 (VE Day) | Tuesday |
The doomsday of each year
On these dates in every year the weekday is the same: 4/4, 6/6, 8/8, 10/10, 12/12, the last day of February, and 5/9, 9/5, 7/11, 11/7 (so it works whichever way your country writes dates). Learn the doomsday of the year and you can find any date’s weekday in your head.
| Year | Doomsday | ISO weeks in the year |
|---|---|---|
| 2024 | Thursday | 52 |
| 2025 | Friday | 52 |
| 2026 | Saturday | 53 |
| 2027 | Sunday | 52 |
| 2028 | Tuesday (leap year) | 52 |
| 2029 | Wednesday | 52 |
| 2030 | Thursday | 52 |
| 2031 | Friday | 52 |
The doomsday moves one weekday on in a common year and two after a leap day – 2027’s Sunday becomes 2028’s Tuesday.
Try it: what day is July 4, 2026? Doomsday 2026 is a Saturday, and 7/11 is a doomsday, so July 11 is a Saturday. July 4 is a week earlier: also a Saturday.
ISO weeks, US weeks and the first week of the year
The ISO 8601 rules: a week runs Monday to Sunday, and week 1 is the one that contains the first Thursday of January (the same thing as the week containing January 4). A year therefore has 52 weeks, or 53 when it starts on a Thursday – or on a Wednesday in a leap year. Days at the very start or end of the calendar year can belong to the neighboring year’s weeks: December 30, 2024 was in week 1 of 2025.
Many US and Canadian calendars use a different system, with weeks starting on Sunday and week 1 starting on January 1, so check which one a schedule or a payroll uses before you match numbers.
Why there are limits
The calculator covers 1900 to 2199. Before 1900, different countries switched from the Julian to the Gregorian calendar in different years – from 1582 in Spain and Italy to 1752 in Britain and its colonies and 1918 in Russia – so an old date’s weekday depends on where it was written.
To see how far away a date is, use days until. Once zet4u is saved on your device, the calculator works offline as well.
Frequently asked questions
What day of the week was I born?
Enter your date of birth above. The answer is in the Gregorian calendar, the one used for civil dates almost everywhere. The age calculator gives the same weekday along with your exact age.
What week number is it?
The calculator gives the ISO 8601 week, used in most of Europe and in business planning: weeks start on Monday and week 1 is the week with the year's first Thursday. So January 1, 2027, a Friday, still belongs to week 53 of 2026. US calendars often count weeks from Sunday and start week 1 on January 1, so their numbers can be one off.
Which years are leap years?
Years divisible by 4, except century years, which must be divisible by 400. 2028 is a leap year; 1900 was not; 2000 was. The rule keeps the calendar within a day of the seasons for about 3,000 years.
What is the doomsday rule?
A mental method by the mathematician John Conway. In every year, 4/4, 6/6, 8/8, 10/10, 12/12, the last day of February, 5/9, 9/5, 7/11 and 11/7 all fall on the same weekday, the year's doomsday. In 2026 it is a Saturday, so 12/12 is a Saturday and Christmas, 13 days later, is a Friday.
Sources
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