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Month Calculator
Count the whole months and leftover days between two dates.
Months are the most awkward unit in the calendar. They range from 28 to 31 days, which means “three months from now” is not a fixed number of days and never has been.
How to count months between two dates
- Pick the start date.
- Pick the end date.
- Press calculate.
- Read the result: whole months, then the leftover days. 15 January to 15 October 2026 is exactly 9 months.
- If the end date comes before the start date, the month count is negative.
The end-of-month problem
A month only counts as complete when the same day number comes round in the next month. That is why 31 January to 28 February 2026 shows as 0 months and 28 days: there is no 31 February, so the first month never closes.
Longer spans work the same way. From 10 March 2025 to 25 September 2026 is 18 whole months, a year and a half, plus 15 days. Contracts and billing systems often define their own end-of-month rule, so check the clause before relying on any count.
Where month counts are used
- Subscription and billing cycles.
- Loan and mortgage terms, which are almost always expressed in months.
- Employment probation periods and notice requirements.
- Warranty and guarantee lengths.
- Age in months for infants, which is how paediatric milestones are tracked.
Months versus weeks
A month is not four weeks. Four weeks is 28 days; an average month is about 30.44. Over a year that difference adds up to a full extra month — which is exactly why there are 13 four-week pay periods in a year but only 12 monthly ones. If you are budgeting, pick one convention and stay with it.
Month calculation questions
How many months are between two dates?
The calculator counts complete calendar months and then reports any remaining days, rather than dividing the total days by 30. That matters because month lengths vary.
How many months are between 31 January and 28 February?
None: the answer is 0 months and 28 days. A month only completes when the same day number comes round again, and February has no 31st, so the span stays in days.
Is a month the same as four weeks?
No. Four weeks is exactly 28 days, while the average month is 30.44 days. The gap accumulates to roughly one extra month across a year.
How many days are in a month on average?
About 30.44, calculated as 365.25 days divided by 12. Useful for rough estimates, but never for a specific date calculation.
What if the end date is before the start date?
The result turns negative. From 15 October 2026 back to 15 January 2026, for example, the calculator shows −9 months.
