How this calculator works
For the month-to-year ratio this page groups exactly twelve months into one year. Converting on to days or seconds uses an average month of 30.4375 days, one twelfth of a 365.25-day Julian year. Those extra equivalents are duration conventions rather than actual calendar dates.
Formula
years = months / 12; months = years x 12. For the supplementary duration outputs, year = 365.25 days.
Worked example
An 18 month plan spans 1.5 years. A 2.25 year plan spans 27 months. Actual dates are needed to find its exact number of calendar days.
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Frequently asked questions
How many years is 30 months?
Two and a half years, because 30/12 = 2.5.
Are all months the same length?
No. Calendar months have different lengths. The supplementary day and second values use an average month.
Is 1.5 years one year five months?
No. Half a year is six months, so it is one year six months.