Month Calculator & Counter
What This Month Tool Does
Adding a month to a deadline sounds trivial until a tricky calendar gets in the way. This calculator adds or subtracts any number of months from a date, and it can also count the months between two dates. Project managers, HR teams, landlords, and anyone juggling subscriptions or contracts reach for it weekly.
Typical uses include warranty expirations, lease milestones, pregnancy and baby timelines, and estimating when a six month subscription renews. Anywhere a contract counts time in months, this tool removes the counting errors.
How Month Math Handles Tricky Days
When adding months, the calculator moves the calendar month forward and keeps the day number whenever it exists. If the target month is shorter, the date clamps to that month's end: one month after January 31 lands on February 28 in a common year, or February 29 in a leap year such as 2024.
Counting between dates works like subtraction on paper: full calendar months are counted first, and any leftover days are shown separately, so February 10 to March 10 is exactly one month even though it spans 28 or 29 days.
Getting Accurate Results Step by Step
First pick a mode under Calculate:, either Months between dates or What is X months from a date. Enter the Start Date, add the End Date when counting, or type the number into Add Months for date arithmetic, using a negative value to move backward, then press Calculate.
Check month end results closely before scheduling payments, because a January 31 due date becomes February 28. Remember that a calendar month is an interval, not a fixed count of days, so three months can total 89 to 92 days depending on which months are crossed.
Frequently Asked Questions
What happens adding one month past January?
Because February never has a 31st, January 31 plus one month clamps to February 28 in a common year. In a leap year like 2024 the result is February 29, and nothing spills over into March.
How do I subtract months from a date?
Enter a negative number, such as -6, in the Add Months field. The calculator steps backward that many months; six months before June 15, 2026, for instance, is December 15, 2025.
Does the count include the start day?
When counting between dates, the span runs from the Start Date to the End Date, so the starting day itself is not counted as part of the elapsed period. If your contract counts the first day, note that convention separately when recording the result.
Are all counted months the same length?
No. A counted month is a calendar month, so one month after March 31 is April 30, not May 1. Consecutive calendar months run from 28 to 31 days, which is why equal month counts can differ in total days.
Can it count months across many years?
Yes. The Months between dates mode handles any Start Date and End Date, whether the two dates sit two months or twenty years apart. Long spans are simply expressed as full months, so ten years equals 120 months.