Cat Age Calculator

Fifteen human years for the first, nine more for the second, then four a year.

Human-equivalent age36 years

Life stageAdult

Actual age5 years

At one year15 human years

At two years24 human yearsnine more, not another fifteen

Each year after that4 human years

A year from now40 human yearsa gain of 4

These figures are the AAFP and AAHA life-stage guidelines. Indoor cats commonly reach 15 to 20 years; outdoor cats average considerably less, and almost all of that gap is traffic, fights and infection rather than ageing.

The formula

first year 15, second year 9 more, then 4 per year

Front-loaded, then steady

A cat reaches roughly a fifteen-year-old human by its first birthday and a twenty-four-year-old by its second, after which each year is worth about four. The first two years are where almost all the development happens, which is why the mapping is a table rather than a multiplier.

Indoor cats live much longer

The difference is not marginal: indoor cats commonly reach 15 to 20 years while outdoor cats average considerably less, and the gap is mostly traffic, fights, infectious disease and predation rather than anything intrinsic. Very few of the causes are ones veterinary medicine can address after the fact.

This does not replace a veterinarian

Every figure on this page comes from a published reference range, and a range is what it stays. The right dose for an individual animal depends on its kidney and liver function, on what else it is taking, on whether it is pregnant or very young or very old, and on what is actually wrong with it — none of which arithmetic can see. Use this to understand the scale of a dose or an exposure, and to have a better conversation with your vet. Do not use it to start, stop or change a medication.

If you believe your animal has swallowed something toxic, do not wait to see whether signs develop. Contact your veterinarian or an animal poison line immediately — in most poisonings the treatment that works is the one given early.