How the calculation works

Size method. A dog’s first year equals roughly 15 human years and the second adds about 9 more, so a two-year-old dog is about 24. After that, each year adds roughly 4 human years for small dogs, 5 for medium, 6 for large and 7 for giant breeds. This mirrors the size-based charts many veterinary practices use.

DNA-based estimate. A 2020 study that compared age-related DNA changes in Labrador retrievers and people proposed human age ≈ 16 × ln(dog age) + 31. It was developed in one breed, applies from about one year of age, and is shown here for comparison only.

Dog age	Small	Medium	Large	Giant
1 year	15	15	15	15
2 years	24	24	24	24
4 years	32	34	36	38
6 years	40	44	48	52
8 years	48	54	60	66
10 years	56	64	72	80
12 years	64	74	84	94
14 years	72	84	96	108

Life stages are approximate. Larger breeds are usually considered senior earlier, which is a good moment to talk to your vet about senior check-ups.

Health and nutrition guides are written against published guidance from the AAHA, WSAVA and AVMA. They are general information, not a substitute for advice from your own veterinarian.