Months Calculator
Count complete months between two dates.
What does Months Calculator do?
Count complete calendar months between two dates, plus the leftover days. Because months vary in length, this uses calendar arithmetic rather than dividing days by an average, which is what contracts and subscriptions require.
How to Use Months Calculator
- 1Pick your datesStart and end.
- 2Read the month countComplete months plus leftover days.
- 3See the breakdownAlso shown as years and months.
Key Features
- Complete calendar months plus the remaining days
- Decimal months for proportional billing
- Total months alongside a years-and-months breakdown
- Correct handling of month-end dates
- Months since and months until modes
Frequently Asked Questions
How are complete months counted?
By calendar, not by average length. From 15 January to 15 March is exactly two months. From 15 January to 14 March is one month and 27 days, because the second month has not completed.
What happens with month-end dates?
31 January to 28 February is counted as zero complete months and 28 days, since 31 February does not exist. Some financial conventions treat month-end to month-end as a full month — check which your contract uses.
Why not just divide days by 30?
Because it drifts. Over a year, dividing by 30 gives 12.17 months rather than 12. Calendar arithmetic gives the answer a person or a contract would recognise.
How many months is 100 days?
Between three and four, depending on which months they span. The exact answer needs a start date, which is why this calculator asks for one.
Dates and times are calculated in your browser using its built-in IANA time zone database. Nothing you enter is transmitted.
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