Days between two dates

Counting the last day, or not

Ask how many days there are from Monday 5 October to Friday 9 October 2026 and two answers are both right. From one date to the other is 4 days: that is how long a parcel took or how many nights a hotel charges. Counting every day on the calendar, both ends included, gives 5: that is how long a conference runs or how many days of leave you are taking.

This is the fence-post problem: five posts, four gaps. Octoolo counts the gaps by default and adds the last day when you switch on Count the last day too. The switch changes all four answers, so with it on, 5 October to 9 October reads 5 days and 5 weekdays.

A rule of thumb: count durations and deadlines (“in 30 days”) without the last day, and count days you are present or absent with it. When a contract, a court or a tax office sets a deadline, read how it says to count. The rules differ, and some start on the day after an event.

Weekdays: Monday to Friday, holidays not removed

The Weekdays answer counts Mondays to Fridays. The first date counts if it falls on a weekday; the last one counts only with the switch on. From Monday 12 October to Friday 23 October 2026 there are 11 days and 9 weekdays. Switch on the last day and it reads 12 days and 10 weekdays, two full working weeks.

Public holidays are not taken out, because they depend on your country, state and employer. Subtract them yourself: from 8 October to 25 December 2026 there are 56 weekdays, and if your office closes for Thanksgiving on 26 November, 55 working days are left. If you work weekends or a different pattern, the weekday count will not fit you, so use the plain day count instead.

Why months make the calendar answer differ

Days are a fixed size; months are not. That is why the Calendar answer is counted on the calendar itself: whole years first, then whole months, then the days left. From 1 January to 31 December 2026 is 364 days, which reads as 11 months and 30 days. Switch on the last day and it becomes 365 days, or exactly 1 year.

The same two months hold different numbers of days depending on the year. From 15 January to 15 March is 59 days in 2026 but 60 in 2028, a leap year with a 29 February. Dividing days by 30 to get months goes wrong for the same reason, so use the Calendar line when someone asks in months.

Clock changes do not move the day count. On the night clocks go forward a day has only 23 hours, and a count done in hours comes up an hour short. Octoolo counts calendar dates, so 2 March to 16 March 2026 is 14 days even in New York, which changed its clocks on 8 March in between.

Other ways to count days on Windows

Windows' own Calculator app has a Date calculation mode that shows the difference between two dates and can also add or subtract days from a date, which Octoolo does in a tool of its own, Days from a date. In a spreadsheet such as Excel, subtracting one date cell from another gives the days between them, and the NETWORKDAYS function counts working days and takes a list of holidays; it includes both end dates, like the switch.

What Octoolo adds is the four answers side by side, one switch that changes all of them at once, and a weekday count without writing a formula. It sits in the same app as the age calculator and the time zone converter, and like the rest of Octoolo it keeps working without a connection and shows no ads.