Month Calculator & Counter

How to use the month calculator

Select one of four tasks, fill in the fields that appear and press Calculate:

• Months between dates: enter a start date and an end date (today by default).
• X months from a date: enter a number of months and the date to add them to (today by default).
• Monthsary: enter the date an event began to see how many months have passed and when the next monthly milestone falls.
• Months since a month & year: pick a month and a year to see how many full months have gone by since then.

Whole months are counted by the calendar, not by dividing days by 30, so the answers line up with how people talk about dates: from the 10th of one month to the 10th of the next is one month, however many days that takes.

How months between two dates are counted

The calculator starts at the earlier date and keeps adding one calendar month for as long as the result does not pass the later date. The number of additions is the count of whole months, and the days left over are the remainder.

whole months = largest N where (start date + N months) ≤ end dateRemaining days = end date − (start date + N months).

Example: from 10 March 2025 to 25 July 2026. Adding 16 months to 10 March 2025 gives 10 July 2026, and 17 months would overshoot to 10 August 2026. So the span is 16 months and 15 days.

The result panel shows three lines: the calendar months, the exact span as months and days, and the date of the next monthsary (the start date plus one more month), together with the number of days from today to that date.

If you enter the dates in the wrong order the tool swaps them for the count. The next-monthsary line is still built from the start date exactly as you typed it. Two identical dates give no result.

What happens at the end of a month

Not every month has a 31st. When adding a month lands on a day that does not exist, the date rolls forward into the following month, the same behaviour as most programming languages. 31 August plus one month is nominally 31 September, which becomes 1 October.

In the second row 31 August plus two months is 31 October, which exists, so the span is exactly two months. In the last row, 31 January plus one month is 31 February, which rolls over to 3 March 2026 (a common year), so reaching 3 March completes the first month.

What is X months from a date

Type the number of months and the date to start from. The answer is shown as year-month-day.

Examples: 18 months after 15 March 2026 is 15 September 2027. One month after 31 January 2026 is 3 March 2026, because 31 February rolls over. Six months after 31 August 2026 is 3 March 2027 for the same reason.

A fractional number of months is cut to a whole number (1.5 months counts as 1), and zero gives no result. Contracts and loans sometimes define a month-end rule of their own, such as always landing on the last day of the month, so check the wording of the agreement before relying on a date.

Monthsary: a monthly anniversary counter

A monthsary is the monthly echo of an anniversary: the same day of each month after something began, such as a relationship, a baby's birth or a first day at a job. Enter the event date and the calculator reports:

• the date and the number of days to the next monthsary, and which numbered monthsary (1st to 12th) it will be
• the time since the event in years, months and days
• the full months, full weeks and total days since the event

The monthsary counter restarts after each year, using only the months left over once whole years are removed. For an event more than a year back, the date it shows can therefore fall in the past, and the days figure is the distance from today either way. For the first mark after any chosen date use the first mode, which adds months to the start date directly. An event date in the future is rejected.

Months since a month and year

This mode counts the full months completed since the end of the chosen month. For example, on 19 October 2026 the answer for March 2024 is 30, and for September 2026 it is 0, because a whole month has not yet passed since the end of September. The current month and any later month are rejected, since they have not finished.

How many months is X days?

Months differ in length, so there is no single answer, but an average month lasts 30.44 days:

months ≈ days ÷ 30.436930.4369 = 365.2425 days in an average Gregorian year ÷ 12

When the exact calendar matters, enter the two real dates in the first mode instead of converting days. Month lengths are 31 days for January, March, May, July, August, October and December, 30 days for April, June, September and November, and 28 or 29 for February (see the leap year calculator).

Which calendar is used

All calculations use the Gregorian calendar, extended backwards in time for earlier dates. Dates in historical sources that predate a country's switch to the Gregorian calendar may not match.

For different units, use the days between dates calculator or day counter, shift a date by days with the add days calculator, or count in years with the years calculator. For wedding or work milestones try the anniversary calculator.