Inclusive versus exclusive counting
From the 1st to the 5th is four days if you count the gaps, or five if you count the days themselves. Neither is wrong — but hotels, leave policies and rental agreements often disagree about which they mean.
Turn on the inclusive option when the end day is itself part of the span, as with a holiday booking or a project deadline that includes the final day.
Why calendar months resist arithmetic
Months are between 28 and 31 days, so "three months" has no fixed length. The years-months-days breakdown above walks the calendar properly rather than approximating, which is why it cannot be derived from the total-day count.
For anything requiring precision — interest accrual, contract terms, notice periods — the total-day figure is the one to use. Calendar breakdowns are for human description.
Counting notice periods and deadlines
Legal and contractual periods usually start the day after the triggering event and include the final day. A "30 days notice" served on the 1st therefore typically expires at the end of the 31st.
Where a deadline lands on a weekend or public holiday, many rules extend it to the next working day. The working-days figure above helps you see whether that applies.
Frequently asked questions
Why do the years-months-days figures not match total days divided evenly? +
Months have different lengths. Three months could be 89, 90, 91 or 92 days depending on which months they are, so the calendar breakdown and the day count cannot be derived from each other.
How many days between two dates, inclusive? +
Turn on the inclusive option, which counts both the start and end days. A Monday-to-Friday span becomes five days rather than four.
Does this handle timezones? +
It works in whole calendar days, so daylight saving changes and timezone offsets cannot shift the result by a day.