Months & Years Calculator
Measure an exact calendar interval, move a date by months or years, and build recurring schedules without letting short months silently change the rule.
Months between two dates
Results are calendar-exact, then cross-checked as total months, weeks and days.
Exact calendar difference
1 year
From the start date to the end date
Full months
12
Total days
365
Weeks + days
52 wk 1 d
Decimal years
1.0000
Add or subtract months and years
The comparison table exposes how each rule handles unavailable dates such as February 30 or April 31.
Result
| Rule | Result | What it means |
|---|
Recurring monthly schedule
Preview renewals, appointments or billing dates and export them.
| # | Date | Day |
|---|
Why month-end rules must be explicit
A month is a calendar unit, not a fixed duration. Native JavaScript rollover can turn January 31 plus one month into a date in March because February cannot hold day 31. That behavior is documented, but it is often surprising.
Clamp is usually clearest for one-off deadlines. Preserve month end is useful for schedules intended to stay on the last day of every month. Rollover is provided when compatibility with overflow-based software matters.
For fixed spans such as exactly 30 or 90 days, use the Days Calculator instead. “One month” and “30 days” are not interchangeable.
Frequently Asked Questions
It depends on the selected rule. “Clamp” returns the last valid day in February. “Preserve month-end” also does that and keeps later occurrences on each month’s final day. “Rollover” carries the extra days into March. The calculator displays all three outcomes so the choice is visible.
Gregorian calendar months contain 28, 29, 30 or 31 days. Calendar-month arithmetic advances the month field and then resolves the day; duration arithmetic adds a fixed number of 24-hour periods. They answer different questions.
The calculator counts full calendar years, then full calendar months, then the remaining whole days. It also reports total full months and total days so you can use the interpretation appropriate to your task.
Yes. The schedule builder supports any whole-month interval, up to 120 occurrences, with the same explicit month-end rule. You can export the dates as CSV or an RFC 5545-compatible iCalendar file.