The 15-9-4 cat-age method
Like dogs, cats age quickly when young and then slow down. Veterinarians widely use a staged conversion rather than a flat multiplier:
year 1 → 15 human years
year 2 → +9 (total 24)
each later year → +4
This reflects how a kitten reaches the equivalent of a teenager by one year old and a young adult by two, after which aging proceeds at a steadier four human years per cat year.
Worked example
A 6-year-old cat:
First 2 years: 15 + 9 = 24 human years.
Remaining 4 years: 4 × 4 = 16.
Human age: 24 + 16 = 40 years.
Quick reference: 1 cat year ≈ 15, 2 ≈ 24, 4 ≈ 32, 7 ≈ 44, 10 ≈ 56, 15 ≈ 76, 20 ≈ 96 human years.
Cat life stages
A cat is a kitten up to about 6 months, a junior to 2 years, prime from 3 to 6, mature from 7 to 10, senior from 11 to 14, and geriatric from 15 onward. Knowing the human-year equivalent helps you anticipate the extra veterinary care that older cats need.