Months and years
A month here is the Gregorian average, 30.436875 days (1/12 of 365.2425 days); real months run 28 to 31 days. Loans, subscriptions, leases and a baby's age are counted in months.
A year here is the Gregorian average of 365.2425 days, which accounts for leap years. Ages, contracts, depreciation and long-term interest are counted in years.
Worked example
Convert 30 mo: 30 × 0.08333333333 = 2.5, so 30 months is 2.5 years. Likewise 20 mo = 1.666666667 yr.
Estimating in your head
Divide by 12 for a quick figure; it is off by about 0%. For 30 mo that gives 2.5 yr, against 2.5 exactly.
Going the other way
To convert years to months, divide by 0.08333333333 (or multiply by 12).
How this works
yr = mo × 0.08333333333
1 mo = 2,629,746 s and 1 yr = 31,556,952 s, both by definition, so the factor is their ratio: 0.08333333333 (rounded here; the page uses the full value). Results drop binary floating-point noise beyond 15 significant digits and display at the precision you choose (6 significant figures by default). Copy result copies the full value.
Frequently asked
How many years are in a month?
1 month = 0.08333333333 years. The factor is exact by definition but has endless decimals, so it is shown rounded; the page uses the full value.
How do I convert months to years?
Multiply by 0.08333333333. For example, 20 mo × 0.08333333333 = 1.666666667 yr.
What is 100 mo in years?
100 mo = 8.333333333 yr. The table next to the converter lists more common values.
Is the result rounded?
Only on screen. The page computes with the exact definitions and removes floating-point noise past 15 significant digits; pick 3 to 12 significant figures, or use Copy result for the full value.
Sources
- BIPM — The International System of Units (SI Brochure), 9th edition
- NIST SP 811 Appendix B.8 — Factors for units listed alphabetically
- Wikipedia — Gregorian calendar
Reviewed Oct 17, 2026 · test vectors fixtures/units/time/months-to-years/