Months Between Dates Calculator
Count full months and days between two dates.
Results update as you type.
How it works
A months between dates calculator works out how many complete calendar months lie between two dates, then how many extra days remain after those whole months. It answers questions like "how many months is this lease," "how long since I started," or "how far apart are these two dates in months," expressed the way people naturally state durations rather than as a large number of days. Counting months is trickier than counting days or weeks because months are not equal in length. A month from 15 January to 15 February is one month, and so is a month from 31 January to 28 February, even though the day counts differ. This calculator follows the calendar-month rule people intuitively use: it counts each time the same day-of-month is reached or passed, and only credits a full month once the end day catches up to the start day. The remaining-days figure fills the gap between the last completed month and the end date, so the two together describe the span exactly, as in "seven months and twelve days." This is the form used for tenancy lengths, loan terms, subscription durations, contract periods and age in months. Landlords and tenants measuring a lease, HR staff computing length of service, and anyone stating a duration in months use a months between dates calculator to get the count right across uneven month lengths.
months = full calendar months from start to end; remainingDays = end − (start + months)
A first estimate of months comes from the difference in years times twelve plus the difference in month numbers. If the end day-of-month is earlier than the start day-of-month, the latest month is not yet complete, so one month is subtracted. The start date is then advanced by that many whole months to form an anchor, and the plain day count from the anchor to the end date gives the remaining days. This mirrors how a full calendar month is only credited once the same day-of-month is reached.
Source:Gregorian calendar / ISO 8601
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter start date and end date.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Full months updates instantly as you type — no button to press.
Frequently asked questions
How are full months counted?
A full month is credited each time the calculation reaches the same day-of-month as the start date. From the 15th to the 15th is one month regardless of whether the month had 28 or 31 days. If the end date's day-of-month has not yet reached the start's, that final month is incomplete and is not counted, with the extra time reported instead as remaining days. This matches how people describe durations like a lease or length of service.
What are the remaining days?
After counting the complete months, the calculator advances the start date by that many months and measures the plain day gap to the end date. That gap is the remaining days, always less than a full month. So a span might be seven months and twelve days, where the twelve days are the part beyond the last whole month. Together the months and remaining days reconstruct the full duration between the two dates.
Why not just divide days by 30?
Because months vary from 28 to 31 days, dividing the total days by 30 gives an approximation that drifts over long spans and disagrees with how contracts count. Calendar-month counting instead tracks the actual day-of-month, so it matches leases, loan terms and age-in-months exactly. Dividing by 30 is fine for a rough estimate, but for anything contractual the calendar method this calculator uses is the correct one.
How does it handle end-of-month dates?
When the start date is late in a long month and the target month is shorter, the count still advances correctly because it compares day-of-month numbers. For example, from 31 January the next monthly milestone falls at the end of February, and the calculator credits the month once February ends and reports any spill-over as remaining days. Very short target months are the classic edge case, and day-of-month comparison handles them consistently.
What if the end date is before the start date?
The calculator treats an end date earlier than the start date as invalid and returns no result, because the months count is defined for a forward span. Enter the earlier date as the start and the later date as the end to measure the duration. If you need the distance in the other direction, simply swap the two dates, and the same months-and-days breakdown applies to that reversed span.