Cat age calculator: cat years to human years

How the calculator works

Human years: the International Cat Care chart

The number comes from the chart of International Cat Care, a UK cat welfare charity. Its rule: the first two years of a cat’s life equal 24 human years, and every year after that adds 4. So a 9-year-old cat is 52 and a 15-year-old is 76.

For the first two years the chart goes by months: 6 months equals 10 human years, 12 months 15 and 18 months 21. Between two rows the calculator draws a straight line.

Life stage: the AAHA/AAFP guidelines

The 2021 Feline Life Stage Guidelines of the American Animal Hospital Association (AAHA) and the American Association of Feline Practitioners (AAFP) name four stages by age: kitten (birth up to 1 year), young adult (1–6 years), mature adult (7–10 years) and senior (10 years and older). A fifth stage, end of life, can come at any age, so the calculator doesn’t show it.

The guidelines call any age grouping arbitrary, since cats vary. International Cat Care uses six stages with other names (kitten, junior, adult, mature, senior, super senior), so its chart and the AAHA/AAFP stage won’t always match.

Cat age chart: cat years to human years

The full International Cat Care chart, with the AAHA/AAFP life stage for each age.

Why “multiply by 7” is wrong

Multiplying by 7 makes young cats too young and old cats too old. Cats grow up fast: by the International Cat Care chart, a 1-year-old cat is 15 in human years, not 7, and a 2-year-old is 24, not 14.

After that the pace slows to 4 human years a year, so the rule of 7 overshoots later in life: a 15-year-old cat would be 105 by it, against 76 on the chart.