Counting inclusively or not
From Monday to Friday is four days if you count the gaps and five if you count the days themselves. Both are correct and they answer different questions — "how long until" wants the gap, "how many days of holiday" wants the count.
Contracts and notice periods usually specify which, and the difference of one day is exactly the kind of thing that ends up in dispute. Both figures are shown.
Adding months is not adding days
One month after 31 January is undefined. The usual convention clamps to the last valid day, giving 28 or 29 February, and that is what is done here. It also means adding a month and then subtracting one does not always return to the original date — 31 January plus a month minus a month is 28 January.
Where exactness matters, count in days.
Frequently asked questions
Should I count the start and end dates?
Depends on the question. "How long until" wants the gap; "how many days off" wants the count, which is one more. Both are shown.
What happens adding a month to 31 January?
It clamps to the last valid day — 28 or 29 February. Which also means adding then subtracting a month may not return you to the same date.
Does it handle working days?
Weekends are excluded when you ask for working days. Public holidays vary by country and are not applied automatically.
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