LifeSpan

Cat Age Calculator

The classic '15 for year one, 9 for year two, 4 per year after' rule, done precisely.

Cat's age (years)

Human-equivalent age

36 years

What you entered

Cat's age: 5 years

1
Years 1–2
15 + 9= 24 years
2
Each year after year 2
+ (3 × 4)= 36 years

Result

Human-equivalent age: 36 years

A 5-year-old cat is roughly equivalent to a 36-year-old human, using the classic 15/9/4 rule — indoor cats tend to live longer and age slightly differently than outdoor cats.

Cat years converted to human-equivalent years

Like dogs, cats mature rapidly in the first two years, then age more slowly and more steadily than dogs do.

Cat age	Human equivalent	Life stage
1	15	Adolescent
2	24	Young adult
3	28	Adult
5	36	Adult
8	48	Mature
10	56	Senior
15	76	Geriatric

The first two years match the dog scale almost exactly, but cats then age more slowly - by 15 years a cat is at 76 against a dog's 89. That difference compounds over a long life and is one reason indoor cats commonly reach 15 to 20 years while few dogs do. Cats also hide illness well and show fewer outward signs of ageing, so the human-equivalent figure is a useful prompt for how often to book a check-up: from about 7 cat years, annual becomes twice-yearly in most veterinary guidance.

It's an approximation

Indoor cats often live longer than outdoor cats, and individual health varies widely — this calculator uses a commonly cited simple aging rule, not a veterinary-grade model tailored to your specific cat.

Cats vs. dogs age differently

After the first two years, cats age a bit more slowly than dogs on a per-year basis (roughly 4 human years per cat year versus 5 for dogs) — one reason well-cared-for indoor cats often live into their late teens or twenties.

Frequently asked questions

My cat is 12 years old — what's that in human years?

Year 1 = 15, year 2 = 9, years 3-12 = 4 each. Total: 15 + 9 + 10×4 = 64 human-equivalent years. Your cat is a 'senior' but many indoor cats live well past this — 20-year-old cats (96 human years) aren't uncommon.

Do indoor and outdoor cats age differently?

Indoor cats typically live 12-18 years; outdoor cats average 2-5 years due to hazards like cars, predators, and disease. This calculator uses the same formula for both, but the practical difference in lifespan is dramatic — an indoor-only lifestyle can effectively double a cat's life expectancy.

At what age is a cat considered 'senior'?

Veterinarians generally consider cats senior at 11 years (~60 human years) and geriatric at 15 years (~76 human years). Senior cats benefit from twice-yearly vet checkups instead of annual ones, and their diet and activity needs shift.