Counting Months the Way Calendars Do

"How many months is it between January 15 and June 15?" — eleven, in calendar terms: February through May are complete, and the boundary day-of-month decides whether the end month counts. This calculator follows the day-of-month rule used by billing cycles and tenancy agreements: a month is complete only when the same day number comes around again.

The Day-Number Boundary

Jan 15 → Feb 15 is one complete month; Jan 15 → Feb 14 is zero complete months and 30 days, even though it is nearly a month long. The rule is deliberately simple — count every full month boundary, and leave the partial days as a remainder. That remainder is exactly what the calculator reports as "remaining days," and it never silently vanishes into a rounded month count.

Three Units, One Span

The same period can be expressed as months (calendar), weeks (fixed 7-day chunks), or days (exact). Because months vary between 28 and 31 days, a month figure and a week figure for the same span will never multiply cleanly into each other — the calculator reports all three so a contract clause, a savings goal, or a due date each gets the unit it needs.