Convert a dog's or cat's age to human years

The job

"One dog year equals seven human years" is a myth — dogs mature far faster early on, and small breeds age more slowly than large ones. The converter applies the common estimate: the first year counts as about 15 human years, the second about 9–10 more, then a per-year step that depends on the animal.

How to do it

Choose dog or cat, pick the dog's size if needed, enter the age, and convert. Half-years work too — enter 0.5 for a six-month-old kitten.

• Cats: about 15 human years at age 1, 25 at 2, then +4 per year.
• Dogs: 15 at age 1, 24 at 2, then +4 (small), +5 (medium), or +6 (large) per year.
• The estimate is interpolated, so 1.5 years lands between the year-1 and year-2 values.

Worked example

A 5-year-old medium dog: 15 (year 1) + 9 (year 2) + 3 × 5 = about 39 human years. A 10-year-old cat: 15 + 10 + 8 × 4 = about 57.

Limits

This is a population-level approximation, not a health assessment — breed, weight, and care shift individual aging, and a vet judges by teeth, eyes, and condition. Use it to get a feel for a pet's life stage, not as a medical figure.