Days Between Dates

There are two defensible answers to the same question and they differ by one. Counting the nights between the dates gives the difference: 1 March to 5 March is four. Counting the days you are present for, including both ends, gives five. Neither is wrong, and which one you want depends on why you are asking — a hotel bill counts nights, a leave request usually counts both the first day and the last.

That is what the include the end date control is for. It is visible rather than assumed, so the number on screen is one you can defend when somebody checks it. The start date and end date can be entered in either order; if the end is earlier than the start, the calculator swaps them and says so rather than returning a negative number.

Weeks are simple: the span in days divided by seven, shown as whole weeks with the leftover days named separately rather than folded into a decimal. Months are not simple, because a month is between 28 and 31 days long and the answer depends on which months your span crosses.

The calculator gives months as calendar months rather than as days divided by thirty. It steps forward from the start date one whole month at a time for as long as the result is still on or before the end date, then reports the remaining days. Stepping from 31 January lands on the last day of February, because there is no 31 February, and the same clamping applies wherever a short month is involved. A figure produced by dividing by thirty will disagree with a calendar for most spans, which is why payroll periods, notice periods and contract terms are all written in calendar months.

The business days figure counts Monday to Friday within the span and the weekend figure counts the Saturdays and Sundays, so the two add up to the plain day count. That split answers the common working question — how many working days there are before a deadline — without needing a separate tool.

What it does not do is remove public holidays. Holidays differ by country, by region and sometimes by employer, and a number that quietly assumed one calendar would be wrong for most people reading it. This calculator would rather be exact about what it counted than approximate about what it guessed, so subtract the holidays that apply to you from the business day figure. It also does not know about a working week that is not Monday to Friday, which is normal in several countries. Everything is computed in your browser from plain calendar dates, with no time zone involved and nothing sent anywhere. To land on a date rather than measure the gap to one, the date calculator adds or subtracts a span from a date you give it.