A one-year-old cat is about 15 in human years, and a two-year-old is about 24.
After that, add roughly four human years for each additional year.
These figures come from the 2021 Feline Life Stage Guidelines published jointly by the American Animal Hospital Association and the American Association of Feline Practitioners — the standard reference vets use, rather than a rule of thumb.
Cat years to human years
The largest single factor in how long a cat lives is not breed. It is whether the cat goes outside. Indoor cats commonly reach thirteen to seventeen years; cats with outdoor access average considerably less, largely because of traffic, disease and predation rather than any difference in biological ageing.
| Cat's age | Indoor | Outdoor | Life stage |
|---|---|---|---|
| 1 | 15 | 23 | Kitten |
| 2 | 24 | 31 | Young Adult |
| 3 | 28 | 38 | Young Adult |
| 4 | 32 | 46 | Young Adult |
| 5 | 36 | 54 | Young Adult |
| 6 | 40 | 61 | Young Adult |
| 7 | 44 | 68 | Mature Adult |
| 8 | 48 | 76 | Mature Adult |
| 9 | 52 | 84 | Mature Adult |
| 10 | 56 | 91 | Mature Adult |
| 11 | 60 | 98 | Senior |
| 12 | 64 | 106 | Senior |
| 13 | 68 | 114 | Senior |
| 14 | 72 | 121 | Geriatric |
| 15 | 76 | 128 | Geriatric |
| 16 | 80 | 136 | Geriatric |
| 17 | 84 | 144 | Geriatric |
| 18 | 88 | 151 | Geriatric |
| 19 | 92 | 158 | Geriatric |
| 20 | 96 | 166 | Geriatric |
Indoor and outdoor columns reflect typical median lifespans of roughly 15 and 8 years respectively. A cat with partial outdoor access sits between the two.
Feline life stages
The 2021 guidelines define four stages: kitten (up to one year), young adult (one to six), mature adult (seven to ten), and senior (ten and over). The guidance shifts at each — senior cats are generally recommended twice-yearly examinations and routine bloodwork, because kidney disease and hyperthyroidism become common and both are far more manageable when caught early.
Cats are also unusually good at concealing illness, which is part of why the calendar matters. A change that would be obvious in a dog is often invisible in a cat until it is advanced.
Why cats live so long relative to their size
Among mammals, body size and lifespan usually correlate — bigger animals live longer. Cats sit well above that line for their weight, as do bats and naked mole rats. The leading explanations involve reduced predation pressure and a relatively slow metabolic rate for their size, though the question remains genuinely open in the research.
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Open the calculatorCommon questions
How old is a 1 year old cat in human years?
About 15, according to the 2021 AAHA/AAFP Feline Life Stage Guidelines. A one-year-old cat is roughly a teenager — physically mature but not fully grown.
How old is a 10 year old cat in human years?
About 56 for an indoor cat. Ten is also where the AAHA/AAFP guidelines classify a cat as senior, and where twice-yearly veterinary examinations are recommended.
Do indoor cats live longer than outdoor cats?
Substantially. Indoor cats commonly reach 13 to 17 years, while cats with regular outdoor access average closer to 8. The difference is mostly traffic, disease and predation rather than a difference in how fast they biologically age.
What is the oldest recorded cat?
Creme Puff, a cat from Texas, is generally recorded as having lived to 38 — far beyond the typical range and not a useful planning figure.
When is a cat considered senior?
At ten, under the current AAHA/AAFP guidelines. Mature adult runs from seven to ten, and the main practical change at senior is a move to twice-yearly check-ups with routine bloodwork.