Day of the Week Calculator
Find the weekday of any date from year 1 to 9999, with the day of the year, ISO week, leap year check, Zeller and Doomsday workings and the next 10 years.
Dates use the Gregorian calendar throughout (proleptic before 1582). Britain and its colonies switched in 1752, Russia in 1918, so historical documents may show a different weekday for early dates.
| Year | Date | Weekday |
|---|---|---|
| 2,027 | Wed, November 10, 2027 | Wednesday |
| 2,028 | Fri, November 10, 2028 | Friday |
| 2,029 | Sat, November 10, 2029 | Saturday |
| 2,030 | Sun, November 10, 2030 | Sunday |
| 2,031 | Mon, November 10, 2031 | Monday |
| 2,032 | Wed, November 10, 2032 | Wednesday |
| 2,033 | Thu, November 10, 2033 | Thursday |
| 2,034 | Fri, November 10, 2034 | Friday |
| 2,035 | Sat, November 10, 2035 | Saturday |
| 2,036 | Mon, November 10, 2036 | Monday |
Enter any date and this calculator tells you the day of the week, whether it is in the past or the future: the day you were born, a historical event or next year's birthday. It also gives the day of the year, the ISO week number and whether the year is a leap year. It shows the working by Zeller's congruence and by Conway's Doomsday rule, so you can check it by hand.
How to use this tool
- Pick a date from year 1 to 9999.
- Read the weekday, the day of the year and the ISO week.
- Follow the Zeller or Doomsday working to see how the answer comes out.
- Look at the table for the same date over the next 10 years, handy for birthdays and anniversaries.
Formula
Zeller: h = (q + ⌊13(m + 1)/5⌋ + K + ⌊K/4⌋ + ⌊J/4⌋ + 5J) mod 7
q is the day of the month, m the month (March = 3 … December = 12, with January and February as months 13 and 14 of the previous year), K the year within the century and J the century. h = 0 is Saturday, 1 Sunday … 6 Friday. The Doomsday rule finds the weekday shared each year by easy dates such as 4/4, 6/6, 8/8, 10/10, 12/12 and the last day of February, then counts from the nearest one.
Example
For 20 July 1969: q = 20, m = 7, K = 69, J = 19. ⌊13 × 8/5⌋ = 20, ⌊69/4⌋ = 17, ⌊19/4⌋ = 4 and 5 × 19 = 95, so h = (20 + 20 + 69 + 17 + 4 + 95) mod 7 = 225 mod 7 = 1, which is Sunday. With the Doomsday rule, 1969's doomsday is Friday, 11 July is a doomsday, and 20 July is 9 days later: Friday + 2 = Sunday.
Frequently asked questions
Why does the same date move one weekday each year?
A common year has 365 days, which is 52 weeks and 1 day, so a date shifts forward by one weekday. After 29 February in a leap year it shifts by two.
Which years are leap years?
Years divisible by 4, except century years that are not divisible by 400. So 2000 was a leap year, but 1900 and 2100 are not.
What is the ISO week number?
ISO 8601 weeks start on Monday, and week 1 is the week that contains the year's first Thursday. Some days in early January can belong to week 52 or 53 of the previous year.
Sources
Last updated:
Page address with these inputs: https://kakao.mobile/tools/day-of-the-week-calculator/
Cite or embed this tool
kakaoCalc. (2026, November 8). Day of the Week Calculator. https://kakao.mobile/tools/day-of-the-week-calculator/
“Day of the Week Calculator.” kakaoCalc, 8 Nov. 2026, kakao.mobile/tools/day-of-the-week-calculator/.
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