About this tool
Pet Age Calculator is a free, in-browser tool that converts your dog or cat's age into an approximate human-equivalent age and labels their life stage. Pick the species, type the age in years (decimals like 0.5 are fine), and everything is worked out locally — nothing is uploaded.
Dogs under one year use human = age × 15. From one year on it uses the 2019 epigenetic-clock formula human = 16 × ln(age) + 31, where ln is the natural logarithm — this reflects that dogs mature fast then slow down. Cats use age-band math: the first year counts as 15, the second adds 9 (human = 15 + (age − 1) × 9), and each year after that adds 4 (human = 24 + (age − 2) × 4). The result is rounded to the nearest whole year.
Use it to gauge whether a pet is a puppy or kitten, an adult, or a senior so you can plan check-ups and diet. Remember it is an approximation: breed and body size change how dogs age, with small dogs generally living longer than giant breeds.