Date difference
A useful answer. A moment of your time.
Choose a start and an end
The end date must be the same as or later than the start date. The default result counts the gap between them: Monday to Tuesday is one day. Two identical dates have an elapsed difference of zero.
Include both dates when you mean a span
Turn on the inclusive option if you want to count every date in the span, including the first and last. Monday through Tuesday then counts as two dates. The result states which convention you selected so you can use it consistently.
Weeks are groups of seven days
The week figure divides the resulting day count into complete groups of seven and a remainder. It does not align the result to Monday-to-Sunday calendar weeks. All weekdays and weekends are included; there is no holiday calendar in this tool.