Convert Years to Months

About converting Years to Months

Years (yr) and Months (mo) are both units of time, so converting between them is a single multiplication: multiply your Years figure by 12. Ten Years comes to 120 Months, and a hundred works out at 1,200 Months.

Rule of thumb: going from Years to Months multiplies, so the figure always grows — one Year is already 12 Months. If your answer came out smaller, you have the conversion the wrong way round.

What is a Year?

There is no single year. A Julian year is exactly 365.25 days; a Gregorian calendar year averages 365.2425 days, because its leap rule drops three leap days every four centuries; and the tropical year — the actual round trip of the seasons — is about 365.2422 days. The leap-year rules exist precisely to stop the calendar drifting away from that tropical figure. This converter uses the Julian year of 31,557,600 seconds, the convention astronomers use and the one the light-year is built on, but it is a chosen convention rather than a fact about the Earth.

What is a Month?

The month is the messiest unit in everyday use. Gregorian months run from 28 to 31 days for reasons that are pure historical accretion rather than design, so there is no true number of seconds in a month at all. This converter uses an averaged month of 2,629,800 seconds — one twelfth of a Julian year, about 30.44 days — and that is a convention, not a definition: the answer here is an average, not a fact. It is worth remembering that a month in a contract or a subscription almost always means a calendar month rather than thirty days, and the difference decides real billing dates.

To put both in perspective: a year is one lap of the Earth around the Sun, while a month is one page of a wall calendar.

The converter above updates as you type, and the table lists common values for quick reference. Need the opposite direction? Use the Months to Years converter, or browse all Time converters.