May 9, 2027 will be a Sunday. It is day 129 of the 365-day year 2027 (236 days remain after it) and falls in ISO week 18. Counting from today in Brasília, that date is in 218 days (31 weeks and 1 day). 2027 is not a leap year.
← May 8, 2027 May 10, 2027 → Moon phase on that day
How to work out the weekday of a date
The calendar repeats a fixed pattern: a week has 7 days, a common year has 364 days plus one extra (52 weeks and 1 day), and a leap year has 2 extra days. So the same date moves forward by one weekday each year and by two after February 29. Computers use this arithmetic directly, counting days from a reference date and taking the remainder after dividing by 7.
Zeller's congruence turns this into a formula for the Gregorian calendar: h = (q + ⌊13(m+1)/5⌋ + K + ⌊K/4⌋ + ⌊J/4⌋ + 5J) mod 7, where q is the day of the month, m the month (March = 3, ..., with January and February counted as months 13 and 14 of the previous year), K the year within the century and J the century. The result h is 0 for Saturday, 1 for Sunday, and so on. Example, September 7, 1822: q = 7, m = 9, K = 22, J = 18, so h = (7 + 26 + 22 + 5 + 4 + 90) mod 7 = 154 mod 7 = 0, which is Saturday, matching the tool.
Conway's Doomsday rule is the favorite of mental calculators. In every year the dates 4/4, 6/6, 8/8, 10/10 and 12/12, plus the last day of February, fall on the same weekday, called the "doomsday". Knowing the doomsday of the year, you only count forward or backward from the nearest anchor date.
The same date in different years
The table shows the weekday of New Year's Day, Independence Day (USA) and Christmas in each year. Notice how a date moves forward one weekday per year and jumps two after a leap year.
| Year | Jan 1 | Jul 4 | Dec 25 | Leap year? |
|---|---|---|---|---|
| 2020 | Wednesday | Saturday | Friday | Yes |
| 2021 | Friday | Sunday | Saturday | No |
| 2022 | Saturday | Monday | Sunday | No |
| 2023 | Sunday | Tuesday | Monday | No |
| 2024 | Monday | Thursday | Wednesday | Yes |
| 2025 | Wednesday | Friday | Thursday | No |
| 2026 | Thursday | Saturday | Friday | No |
| 2027 | Friday | Sunday | Saturday | No |
| 2028 | Saturday | Tuesday | Monday | Yes |
| 2029 | Monday | Wednesday | Tuesday | No |
| 2030 | Tuesday | Thursday | Wednesday | No |
What else the tool shows
Day of the year counts from January 1 (day 1) up to December 31 (day 365 or 366). The ISO week number follows ISO 8601: weeks run from Monday to Sunday and week 1 is the week with the year's first Thursday, so a few days at the start or end of a year may belong to a neighboring year's week. The distance from today uses the Brasília date, so it does not depend on your device's time zone. A year is a leap year when it is divisible by 4, except century years not divisible by 400, which is why 1900 was not a leap year and 2000 was.
To work with dates further, use the days between dates calculator, the date calculator to add or subtract time, the week number page or find the Moon phase on the day you were born.