What this calculator does
It answers questions like "how many Mondays are left this year?", "how many Fridays are in October?" or "how many Sundays between two dates?". That's useful for counting classes or gym sessions on a set day, weekly paychecks, trash pickups or rent due every Friday. Both the start and the end date are counted.
How it's counted
Any stretch of days splits into full weeks plus a few extra days. Each full week has exactly one of every weekday, so only the extra days need checking:
Count = ⌊days ÷ 7⌋ + (1 if the chosen weekday is among the leftover days, else 0)
To find the first one, move forward from the start date by (chosen weekday − start weekday) mod 7 days. Every later one is 7 days after the previous.
Worked example: Mondays from October 27 to December 25, 2026
October 27, 2026 is a Tuesday and December 25 is a Friday. That's 60 days counting both ends: 8 full weeks (56 days) plus 4 extra days, Tuesday to Friday. The extra days don't include a Monday, so the answer is 8 Mondays. The first is November 2 and the last is December 21. The same span has 9 Tuesdays, because the extra days start on a Tuesday.
How many of each weekday are in a year?
A common year is 52 weeks and 1 day, so the weekday of January 1 happens 53 times and every other weekday 52 times. A leap year is 52 weeks and 2 days, so the weekdays of January 1 and January 2 each happen 53 times.
| Year | January 1 is a | Weekdays that occur 53 times |
|---|---|---|
| 2025 | Wednesday | Wednesday |
| 2026 | Thursday | Thursday |
| 2027 | Friday | Friday |
| 2028 (leap year) | Saturday | Saturday and Sunday |
A month has 4 of each weekday plus 0 to 3 extras: 28 days gives exactly 4 of each, while a 31-day month has three weekdays that happen 5 times.
Limitations
- Holidays aren't removed. To count business days without US federal holidays, use days between dates.
- Both end dates always count. If you want to leave out the start or end date, move it by one day.
- Dates use the Gregorian calendar, extended backward before 1582.