Show the difference between two dates and times as a Y/M/D H:M:S breakdown, plus totals in days, hours, minutes, seconds, and weeks
It counts up years, months, and days along the calendar from the start to the end. Because months have different lengths, "1 month" means one calendar month (28-31 days). The total days figure is exact, derived from the millisecond difference.
That is fine. If the start is later than the end, the tool automatically swaps them, notes that it did, and shows the difference as a positive value.
No. The calculation runs entirely in JavaScript in your browser. Your input is never sent to or stored on a server.