Months between dates
Work out how many complete calendar months are between two dates — also shown as years, months and days — for ages, tenure, warranty periods, tenancies or subscription lengths.
Result
Complete months
As whole years
Plus months
Plus days
How to use this tool
- Enter the start date.
- Enter the end date.
- Read the complete months, and the same span as years + months + days.
Assumptions
- Counts whole completed months only — a period of, say, 3 months and 10 days is reported as 3 months, not 3.3.
Technical details: what the fields mean
- Start date
startDate - The earlier date.
- End date
endDate - The later date.
Methodology
Counts complete calendar months — a month only counts as complete once the end date's day-of-month reaches or passes the start date's day-of-month. Extra days are counted from the start date moved forward by those whole months (using the month's last day if it has no matching date, e.g. 31 → 30 April).
Worked example
20 Jan 2026 to 15 Apr 2026
Inputs: Start date: 2026-01-20, End date: 2026-04-15
Result: 2 complete months + 26 days; the third month isn't complete because the end day (15) is before the start day (20).
Age of a child born 15 March 2024 on 12 October 2026
Inputs: Start date: 2024-03-15, End date: 2026-10-12
Result: 30 complete months = 2 years, 6 months and 27 days.
A 12-month tenancy starting 1 Sep 2026 — how long by 31 Aug 2027?
Inputs: Start date: 2026-09-01, End date: 2027-08-31
Result: 11 complete months + 30 days; the 12th month completes on 1 Sep 2027.
Month-end start: 31 Jan 2026 to 28 Feb 2026
Inputs: Start date: 2026-01-31, End date: 2026-02-28
Result: 0 complete months + 28 days — February has no 31st, so a full month from 31 Jan isn't reached until March.
Practical guidance
- For notice periods and contracts, check whether the agreement defines a month as a calendar month and which day it ends on; this tool uses the common 'same day next month' rule.
- For an age in years, the 'whole years' figure is the age; months and days give the detail.
Common mistakes
- Approximating months as days ÷ 30, which drifts noticeably over several months since real months vary from 28 to 31 days.
FAQs
Does this count every calendar month touched by the dates?
No. It counts complete months from the start date's day-of-month to the same day-of-month. For 20 January to 15 April, only 2 complete months have elapsed; it does not count January, February, March and April as four inclusive month labels.
How do I work out an age in years, months and days?
Enter the date of birth as the start and today as the end. Whole years is the age; the months and days show how far into the next year.
What happens if the start date is the 31st?
Shorter months have no 31st, so from 31 January the first complete month only shows from 1 March. On 28 February you'll see 0 months + 28 days.
Last reviewed: 2026-10-11
Uses the 'same day next month' convention; legal or contractual definitions of a month may differ, so follow the governing wording where it matters.
This tool provides an indicative estimate, based on the assumptions stated above.
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