Date range duration
The span between two dates expressed every way at once: years, months and days, plus the totals in days, weeks, months and hours.
How to use the date range duration
Having every unit at once avoids the commonest mistake in date arithmetic, which is quoting a figure in the wrong one. "Three months" and "90 days" are different spans and a contract that uses them interchangeably has a problem; showing both makes the difference visible rather than something you have to remember to check. The direction field matters for the same reason: reversing the dates gives the same magnitude with the opposite sign, and a duration that comes out negative usually means the inputs are the wrong way round rather than that anything is wrong with the arithmetic.
Questions
Because quoting a span in the wrong unit is the commonest date mistake. Three months and ninety days are not the same span.
Because a month is not a fixed length. Counting calendar months from 31 January to 1 March gives one month and one day; dividing the days by 30.44 gives 1.02. Neither is wrong, they answer different questions.
You get the same magnitude with the direction reversed. That usually means the inputs are the wrong way round.
The count is between the dates, so a range from the 1st to the 2nd is one day.
Your device’s. The calculation runs in your browser, so it is today where you are rather than on a server somewhere else.