To calculate the number of days between two dates, subtract the earlier date from the later date. That standard difference counts the days you cross, so 1 June to 2 June is one day. If you need an inclusive count that includes both 1 June and 2 June, add one.
Start by deciding what you are counting
Write the earlier and later dates in the same format, including the year. Then decide whether your question is about elapsed time or calendar dates touched. Elapsed time usually excludes the starting date. A hotel stay from Monday to Tuesday is one night; a two-day attendance list may include both Monday and Tuesday.
Use a small example
From 10 March to 15 March, the elapsed difference is five days: 11, 12, 13, 14 and 15 March. An inclusive count is six because it also includes 10 March. Stating the rule beside the result prevents a perfectly correct number from being misunderstood.
Remember months and leap years
Months contain 28, 29, 30 or 31 days, so multiplying a month count by 30 is only an estimate. Leap years add 29 February. A reliable date calculator handles those boundaries for you, but the inclusive-or-exclusive choice still belongs to you.
Make the result useful
Use the answer to set a preparation reminder rather than treating it as trivia. A deadline 42 days away may call for a first check-in now and another nearer the date. Save the meaningful date in Daytely with a label that says what must happen next.
Questions people ask
Do I count the starting date?
Count it only when your situation uses inclusive dates. For elapsed time, leave it out.
Can I count backwards?
Yes. Put the earlier date first for a positive duration, or keep the sign if direction matters.
