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Dog Age in Human Years

You've probably heard that one dog year equals seven human years. It's a handy idea, but it isn't accurate. The American Veterinary Medical Association says dogs do not age at a rate of seven human years for each dog year.

Dogs grow up very fast in their first two years, then age more steadily. Size matters too. Larger dogs tend to have shorter lives than smaller dogs, so they reach old age sooner.

Dog Age Chart by Size

This chart comes from a Zoetis poster published on the American Animal Hospital Association website, adapted from the Dog Owner's Home Veterinary Handbook. It compares a dog's age with a rough human equivalent based on adult weight.

Dog's age Up to 20 lb (9 kg) 21 to 50 lb (10 to 23 kg) 51 to 90 lb (23 to 41 kg) Over 90 lb (41 kg)
1 year 15 15 15 15
2 years 24 24 24 24
3 years 28 28 30 32
5 years 36 37 40 42
7 years 44 47 50 56
10 years 56 60 66 78
12 years 64 69 77 93
15 years 76 83 93 115

Treat these as rough guides only. Breed, health and lifestyle all affect how a dog ages, and your vet is the best person to judge your own dog.

The DNA Formula

In 2020, researchers at the University of California San Diego compared age-related chemical changes in the DNA of dogs and people. They came up with this formula.

Human age = 16 x ln(dog's age) + 31

Here "ln" means the natural logarithm, which most phone calculators can work out. By this measure, a one-year-old dog is similar to a 30-year-old person, and a four-year-old dog is similar to a 52-year-old. The researchers noted one limitation. The study used only Labrador Retrievers, and some breeds live longer than others, so it may not fit every dog equally well.

When Is a Dog a Senior?

There's no single age, because it depends on size. Experts suggest a dog counts as senior in the last 25 percent of the expected life span for its breed. Using American Kennel Club data, the AVMA gives these rough ages.

Size Senior from about
Small or toy, under 20 lb (9 kg) 8 to 11 years
Medium, 20 to 50 lb (9 to 23 kg) 8 to 10 years
Large, 50 to 90 lb (23 to 41 kg) 8 to 9 years
Giant, over 90 lb (41 kg) 6 to 7 years

Senior dogs benefit from vet checks twice a year or more, so problems can be found early. Watch for changes in weight, mobility, sleep or behavior, and mention them to your vet.

See also Feeding Puppies and Dogs by Age, Vaccinations and Dog Breeds.

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