How complete months are calculated
Starting from the earlier date, the calculator steps forward one calendar month at a time. A complete month is counted each time the same day-of-the-month is reached (or the last day of the month, when the starting day does not exist in the target month — for example, 31 January plus one month lands on 28 or 29 February). After all complete months are counted, any remaining days are tallied separately.
The total day count is calculated independently using the raw difference between the two dates. This number is always unambiguous, unlike the months count, which depends on how the calendar month boundary is defined. Both figures are reported so you can choose the one that suits your purpose.
Complete months = Calendar month steps from start date to largest date ≤ end date
Remaining days = end date minus the date reached after those months.
Total days = End date (Julian day number) − Start date (Julian day number)
A direct day count unaffected by month-length variation.