Cat Age Calculator

Cat years to human years using the veterinary life-stage chart, from a birthday or an age, and in reverse. Kittens in weeks and months handled properly.

The chart

Where the numbers come from

The chart is the one in the 2021 AAHA/AAFP Feline Life Stage Guidelines, which most veterinary practices use: a cat's first year is worth about 15 human years, the second brings it to 24, and each year after adds about four. It is a convention for thinking about life stage and care, not a measurement. Unlike dogs, cat ageing does not vary much by breed or size, so there is no size adjustment here.

For kittens the calculator interpolates inside the first year so a 3-month-old is not reported as "0 years." The first year is split roughly as: 1 month ≈ 1, 3 months ≈ 4, 6 months ≈ 10, 12 months ≈ 15 human years, which tracks the common vet chart.

Life stages and what they mean

Kitten (0–1 year): growth, vaccination series, neutering. Young adult (1–6): peak condition; weight gain is the thing to watch. Mature adult (7–10): the guidelines recommend annual bloodwork from here because kidney and thyroid changes start to appear. Senior (10+): twice-yearly checks; dental disease, arthritis and chronic kidney disease are common. Indoor cats routinely reach 15–18; the oldest verified cat, Creme Puff, lived to 38 (about 168 human years by this chart, which tells you the chart was not built for outliers).

Human to cat years

The reverse tab answers "if I were a cat, how old would I be?" It inverts the same chart: under 15 is scaled inside the first cat year, 15–24 is the second year, and above 24 every four human years is one cat year. A 40-year-old human is a 6-year-old cat.

Source: AAHA/AAFP Feline Life Stage Guidelines (Quimby et al., 2021, J Feline Med Surg 23:211–233).