Inclusive or exclusive?
From 1 January to 31 March 2026 there are 89 days if you count the gap between the dates, and 90 days if both the first and last day count. A hotel stay counts nights (the gap); a holiday from Monday to Friday “inclusive” counts both ends (5 days, not 4).
In the Date Difference Calculator, tick Include the end date when both days should count.
Count calendar days
- Choose the option for the time between two dates.
- Enter the start and end dates.
- Decide whether to include the end date.
- Read the total days and the same period in weeks, months and years.
Count working days
The calculator also shows business days — Monday to Friday. From 1 January to 31 March 2026 inclusive there are 64 weekdays. Public holidays vary by country and region, so they are not built in: list any that apply, one date per line, and they will be skipped.
If your weekend is not Saturday–Sunday (for example Friday–Saturday), adjust the result manually.
Find a deadline: add or subtract days
Switch to adding or subtracting days, enter a start date and a number of days, and choose calendar days or business days. For example, “payment due within 30 days of the invoice date” uses calendar days, while “delivery in 7 working days” uses business days and skips listed holidays.
Days in each month
Most counting mistakes come from assuming every month has 30 days.
| Days | Months |
|---|---|
| 31 | January, March, May, July, August, October, December |
| 30 | April, June, September, November |
| 28 or 29 | February (29 in leap years) |
So “one month” from 31 January is not 31 February: calculators and contracts usually move it to the last day of February. “30 days” and “one month” are therefore not the same period, so check which one a contract or notice uses.
Legal and contractual deadlines
Courts and contracts sometimes have specific counting rules, such as excluding the day a notice was served or extending a deadline that falls on a holiday to the next working day. Use the calculator for the arithmetic, and check the rule that applies to you. To calculate someone’s age on a date, use the Age Calculator instead.
Frequently asked questions
How many days are in a year?
365, or 366 in a leap year. Leap years are divisible by 4, except century years not divisible by 400 — so 2000 was a leap year and 2100 will not be.
How many working days are in a year?
A year has 260 or 261 weekdays (262 in some leap years), before subtracting public holidays.