Cat Age Calculator
Your cat’s age in human years, and — more usefully — the life stage a veterinarian would act on. One table covers every cat, and indoor living changes how long the cat is likely to live without changing how fast it ages.
How old is your cat?
Kittens are usually described in months, and the first year is where the curve is steepest.
Decimals are fine. A rescue cat with no history is usually aged from its teeth, so treat that number as an estimate.
This changes the life expectancy shown, not the age conversion. An outdoor cat does not age faster; it is exposed to more that can kill it.
A cat of 5 years is in the young adult stage. The first year is worth about 15 human years and the second about 9, so a two-year-old cat is roughly 24; every year after that adds about 4. Living indoors, expect 12 to 18 years.
- Life stage
- Young adult
- Stage covers
- 1 to 6 years
- Age in cat years
- 5 years
- Next stage
- Mature adult at 7 years
- Life expectancy
- 12 to 18 years
- What the stage changes
- Annual exam, dental check, and a body condition score on the record.
| Cat age | Human-age equivalent | Life stage |
|---|---|---|
| 1 yr | 15 | Young adult |
| 2 yr | 24 | Young adult |
| 3 yr | 28 | Young adult |
| 4 yr | 32 | Young adult |
| 5 yr | 36 | Young adult |
| 6 yr | 40 | Young adult |
| 7 yr | 44 | Mature adult |
| 8 yr | 48 | Mature adult |
| 9 yr | 52 | Mature adult |
| 10 yr | 56 | Senior |
| 11 yr | 60 | Senior |
| 12 yr | 64 | Senior |
| 13 yr | 68 | Senior |
| 14 yr | 72 | Senior |
| 15 yr | 76 | Senior |
| 16 yr | 80 | Senior |
| 17 yr | 84 | Senior |
| 18 yr | 88 | Senior |
| 19 yr | 92 | Senior |
| 20 yr | 96 | Senior |
- One table covers every cat. Unlike dogs, cats show no size-class effect — a Maine Coon and a Siamese are on the same curve, so breed and weight are not inputs here.
- Indoor versus outdoor is a life expectancy figure, not an ageing rate. The gap is traffic, fights, predation and infectious disease — causes of death, not faster senescence.
- The life stage is the part with clinical consequences. It is what decides which screening tests are worth running, which is why the profession replaced cat-years arithmetic with it.
Fifteen, then nine, then four a year
A cat packs an extraordinary amount of development into its first year: birth to sexual maturity, full skeletal growth and most of its adult behaviour. That year is conventionally worth about 15 human years. The second year completes social maturity and is worth about 9 more, putting a two-year-old cat at roughly 24. After that a domestic cat ages slowly and evenly, at about 4 human years per calendar year.
human age = 15 + 9 + (age − 2) × 4 • for age over 2- age
- The cat’s age in calendar years
- 15
- The first year — birth to full sexual maturity
- 9
- The second year, which completes social maturity
- 4
- Every year after, for the rest of the cat’s life
The first two years are interpolated rather than stepped, so a six-month-old kitten reads as 7.5 rather than waiting for its birthday to jump to 15. That matters more for cats than for most animals: something like a fifth of the human-equivalent lifespan happens before the cat is old enough to be called anything but a kitten.
Notice what is not in the formula. There is no size class, because cats do not have one — that is the substantive difference between this page and the dog version, where a giant breed ages almost twice as fast as a toy one. And there is no lifestyle term, because indoor living does not slow ageing down.
A five-year-old indoor cat
Fifteen for the first year, nine for the second: 24 at age two. Three more years at 4 each adds 12, so a five-year-old cat is about 36 in human terms. She is a young adult under the AAHA/AAFP stages, which is the stretch where a cat needs an annual exam, a dental check and an honest body condition score, and not much else.
Run the same cat forward. At seven she reads 44 and crosses into mature adult, which is where blood pressure, thyroid and kidney values start earning their place on the bloodwork panel. At ten she reads 56 and is a senior. At fifteen — well within reach for an indoor cat — she reads 76.
Compare that with multiplying by seven, which would make her 35 at five and 105 at fifteen, and would make a one-year-old cat a seven-year-old child. A one-year-old cat can already have raised a litter.
Life expectancy, not ageing rate — the distinction matters
Indoor cats commonly live 12 to 18 years, and a meaningful number pass 20. Cats with outdoor access average considerably less. It is tempting to fold that into the conversion and say an outdoor cat is “older” per year, and it would be wrong.
The gap is made of traffic, fights and the infections they transmit, predation, poisoning and untreated injury. Those are causes of death, not mechanisms of senescence. An outdoor cat that reaches twelve is exactly as aged as an indoor cat that reaches twelve — she simply had a lower probability of getting there. So this calculator moves the life expectancy band when you change lifestyle and leaves the human-age figure untouched, which is the only honest way to represent a difference in mortality rather than in ageing.
Read the outdoor band loosely. Published figures vary enormously depending on whether “outdoor” means a cat with a flap and a garden or an unowned free-roaming cat, and averages that mix the two get quoted far more confidently than the underlying data supports. It is a population average that includes cats killed at two and cats that reach eighteen — not a prediction about yours.
What this calculator assumes
- One curve for every cat. No breed, no weight, no size class — because the evidence for a size effect in cats is not there the way it is in dogs.
- The 15 / 9 / 4 pattern is a widely used convention rather than a fitted model. There is no feline equivalent of the canine epigenetic curve in general use, so treat the output as accurate to within a few human years.
- Life stages follow the 2021 AAHA/AAFP boundaries: kitten under 1, young adult 1 to 6, mature adult 7 to 10, senior 10 and over. The guidelines also describe an end-of-life stage that can occur at any age, which no calculator should attempt to predict.
- Life expectancy bands are population averages for the lifestyle, not a forecast for an individual animal, and they do not adjust for neuter status, indoor enrichment or existing disease.
- Nothing here is veterinary advice. If the age you entered was itself an estimate from a shelter or a rescue, everything downstream of it inherits that uncertainty.
Cat age FAQ
Do bigger cats age faster, the way bigger dogs do?
No, and this is the biggest single difference between ageing a cat and ageing a dog. Dogs span a 4 lb Chihuahua to a 200 lb mastiff, and larger breeds demonstrably age faster and die younger, so every canine chart splits by weight. Domestic cats cluster between roughly 8 and 12 lb, and a Maine Coon is not on a different curve from a Siamese. One table covers the species, which is why this calculator asks for no breed and no weight. Body condition still matters clinically — an overweight cat carries real risk — but it is not an ageing rate.
Do indoor cats really live longer than outdoor cats?
On average, clearly yes — but the reason is not that outdoor cats age faster. A five-year-old cat with a cat flap and a five-year-old cat that has never left the flat are exactly the same age biologically. What differs is the chance of reaching ten: cars, fights, predators, infectious disease and poisoning are causes of death, not accelerated senescence. That is why this page moves the life expectancy figure when you change lifestyle and leaves the human-age conversion alone.
What is a 'mature adult' cat, and why does the stage matter more than the number?
The 2021 AAHA/AAFP guidelines define four stages — kitten under 1, young adult 1 to 6, mature adult 7 to 10, senior 10 and over — and they exist because a converted human age tells a veterinarian nothing useful. A mature adult gets blood pressure measured, thyroid checked and kidney values watched; a young adult mostly gets a dental check and a weight recorded. The profession replaced cat-years arithmetic with life stages precisely because the stage determines what is worth screening for and the number does not.
How does a vet age a rescue cat with no history?
Mostly by the mouth. Deciduous teeth, then the eruption of adult teeth, dates a kitten fairly precisely up to about seven months. After that it is tartar, gum recession and tooth wear, which are far softer signals — diet and dental care move them years in either direction. Older cats also show iris changes and a coarser coat. Expect an estimate to a band rather than a birthday: 'three to five' is a normal answer, and it is why the age you enter above may itself be a guess.
Is the 15, then 9, then 4 pattern exact?
No — it is a convention that fits observed feline development well, not a fitted curve from a published dataset the way the canine epigenetic formula is. The first year covers everything from birth to full sexual and skeletal maturity, which is genuinely worth about 15 human years; the second year adds the rest of social maturity, about 9; after that a domestic cat ages slowly and steadily. Treat the output as a band of two or three years either side, and treat the life stage as the reliable part.
When should I start treating my cat as old?
At ten, when the guidelines say senior — but the useful change happens earlier, at about seven. That is when twice-yearly examinations, blood pressure and baseline bloodwork start paying for themselves, because chronic kidney disease and hyperthyroidism are both common in older cats and both are far more manageable when caught before the cat looks unwell. Cats are unusually good at hiding illness, which is the whole argument for screening on a schedule rather than on symptoms.
Sources and review notes
- 2021 AAHA/AAFP Feline Life Stage Guidelines — the four-stage model and the screening recommendations attached to each stage
- International Cat Care — feline life stages, indoor and outdoor welfare, and ageing cats
The conversion is a fixed convention rather than data that goes stale. The life stage boundaries are quoted directly from the 2021 guidelines; the expectancy bands are the ranges those bodies publish, deliberately shown as ranges because a single average would imply a precision the underlying figures do not have.