Date Difference Calculator
Counting days across months and years is not simple subtraction: month lengths vary, leap years intervene, and there is a real question about whether both end dates count. This calculator handles all three.
Formula
Days between = end date − start date
- Working days exclude weekends, and public holidays vary by nation
- A leap year is divisible by 4, except centuries not divisible by 400
1 January to 31 December in a non-leap year is 364 days
Inclusive or Exclusive?
How many days from Monday to Friday? Four if you are measuring the gap, five if you are counting the days themselves.
Neither is wrong. A hotel stay is four nights but touches five days. Use the exclusive count for elapsed time and the inclusive count when counting occurrences — days worked, nights stayed, days attended.
Calendar Days Versus Working Days
Removing weekends changes the picture substantially. From 2 September to 25 December 2026 there are 114 calendar days but only 82 working days.
Note that the working-day count removes Saturdays and Sundays but not public holidays, which vary by country. England and Wales normally have eight bank holidays, so an annual weekday count of 261 is really about 253 working days.
Why Months Are Ambiguous
The years, months and days breakdown works by borrowing the length of the preceding month, which is why "one month from 31 January" has no single correct answer. When precision matters — contracts, deadlines, interest — work in total days rather than months.
Quick Reference
| Span | Days | Weeks | Working days |
|---|---|---|---|
| 1 week | 7 | 1 | 5 |
| 1 month (30 days) | 30 | 4.3 | ~22 |
| 1 quarter | ~91 | 13 | ~65 |
| 1 year | 365 | 52.1 | ~261 |
| 1 leap year | 366 | 52.3 | ~262 |
Frequently Asked Questions
- Should I include the end date?
- Include it when counting days as occurrences, such as days worked or nights stayed. Exclude it when measuring elapsed time between two points.
- Are bank holidays excluded from working days?
- No. Weekends are removed but public holidays are not, because they differ by country and year. Subtract your own jurisdiction’s holidays manually.
- How do leap years affect the count?
- A year is a leap year if divisible by 4, except centuries, unless divisible by 400. So 2000 was a leap year but 1900 was not and 2100 will not be.
- Why does the month count look wrong?
- Because months have unequal lengths, the breakdown borrows from the previous month. For unambiguous results use the total day count.