What next?
Months into years is one conversion of a duration.
How to use this converter
- Type the value you want to convert.
- Pick the unit it is measured in.
- Read that same amount of time in every other unit at once.
What your result means
Every unit of time is just a multiple of the second, so the converter turns your value into seconds first, then divides into each other unit. Days and below are exact; months, years and above use averages — a year of 365.25 days (to include leap years) and a month of that year divided by 12 — so long spans stay consistent rather than swinging with the calendar.
Why this one is different
One duration is opened out along the whole ladder at once — milliseconds through seconds, minutes, hours, days, weeks, months, years and decades to millennia — so a figure quoted in any of them can be checked against the rest. The month and year rows name the average lengths they use, neither being a whole count of days.
Why the second is the anchor
The second is the SI base unit of time, and every other unit — from a millisecond to a millennium — is defined as a fixed number of seconds. Converting through seconds means you can hop between any two units with a single multiply and divide, no matter how far apart their scales are.
Formula
Example conversion
Converting 30 months to years:
30 × 2,629,800 ÷ 31,557,600 = 2.5 years
How long each unit is
Why a month is the most slippery unit in the calendar
Seconds, days and weeks are fixed. Months are not: they run from 28 to 31 days, so any conversion between months and smaller units has to pick an average. This tool uses 30.44 days, which is 365.25 divided by 12 — the figure that makes a year of months come out exactly right even though no individual month matches it.
That approximation is fine for planning and wrong for contracts. A loan quoted at 36 months does not run for 36 lots of 30.44 days; it runs to the same date three years later, whenever that falls. Interest accrual, notice periods and subscription renewals all work on calendar dates, not on averaged month lengths, so use a date calculator rather than a unit conversion whenever the exact day matters.
Where the average is genuinely useful is comparing rates. A £15 monthly subscription is £180 a year, not £195, because there are 12 months and not 13. A £3.50 weekly one is £182 a year, because there are 52.18 weeks. Converting both to the same annual figure is the only way to see that the two are within £2 of each other.
Frequently asked questions
How many seconds are in a year?＋
About 31,557,600 seconds, based on an average year of 365.25 days to allow for leap years.
Why isn’t a month exactly 30 days?＋
Calendar months range from 28 to 31 days. This converter uses an average month of about 30.44 days (a year ÷ 12) so conversions stay consistent.
How many months are in a year for calculation purposes?＋
Twelve exactly, so 30 months is 2 years and 6 months. Only conversions involving days or weeks need average-length assumptions.
What average month length does this use?＋
About 30.44 days, which is 365.25 divided by 12. That average is what makes month-to-day conversions approximate rather than exact.
Is this suitable for a baby's age?＋
For a rough figure, yes. Health professionals track infants in completed weeks or months from the birth date, so use the age calculator for anything that needs exact dates.
How do I convert months to weeks?＋
Multiply by roughly 4.35, not 4. Using 4 weeks per month loses about two weeks a year, which is why loan and rent schedules never work that way.
Related calculators
Assumptions & limitations
Converting between time units needs a convention for the awkward ones:
- A year is taken as 365.2425 days — the Gregorian average — and a month as one twelfth of that, about 30.44 days. Calendar months are 28–31 days, so month conversions are averages, not exact counts.
- For a specific date range, use the date difference calculator instead: it counts real days rather than applying an average.
- Weeks, days, hours, minutes and seconds convert exactly; only months and years involve an approximation.