Dog Age Calculator: Dog Years to Human Years by Size

This dog years calculator takes your dog's age and adult size. You get the age in human years two ways, plus life stage.

By the Dog Age Tools team · Facts checked against the AVMA, the AKC and peer reviewed studies · Math covered by unit tests · Last updated October 22, 2026 · Our method

Not veterinary advice. These tools give estimates for general interest. Your dog's health, weight and care plan should come from a licensed veterinarian who has examined your dog.

How do you convert dog years to human years?

Start with size. For a medium dog, the first year equals about 15 human years. The second year adds about 9 more, for a total of 24. After that, each year adds about 4 or 5. Small dogs age a bit slower after year five, and large and giant dogs age faster.

That rule comes from the American Kennel Club, which credits the American Veterinary Medical Association (AVMA).

Two methods, two answers

The tool shows two numbers because experts use two different ideas of age.

1. The size chart (AVMA guide)

This method looks at growth and life span. Small dogs often live longer than big dogs, so their later years count for less. The AVMA notes that larger breeds tend to have shorter life spans, and it sets senior age by size. The chart below uses this approach. Between whole years, the tool moves in a straight line, so 6 years and 6 months lands halfway between age 6 and age 7.

2. The DNA clock (UCSD, 2020)

In 2020, a team led by Tina Wang and Trey Ideker at the University of California San Diego published a study in Cell Systems. They studied DNA methylation, a set of chemical tags that build up on DNA as we age. They compared blood from 104 dogs, mostly Labrador Retrievers aged 0 to 16, with data from 320 people.

Human age = 16 × ln(dog age) + 31

Here ln is the natural log, and dog age is in years. A 1 year old dog is about 31. A 4 year old is about 53. A 12 year old is about 71. The authors found the curve lines up with real life events. A dog at 8 weeks matches a baby of about 9 months, when both start to get baby teeth. The average Lab life span of 12 years lines up with a human life span of about 70 years.

Which method should you use?

Use the size chart for most dogs, and always for small or giant breeds. It accounts for size, which is the biggest factor in how fast dogs age. Use the DNA clock as a second view for Labs and other dogs near Lab size. It was built from Lab blood samples, so it fits them best.

Small breeds: the DNA clock may overstate age, since small dogs often live past 14.
Giant breeds: both methods can understate age. Many giant dogs are senior by 6 or 7.
Puppies under 8 weeks: the DNA formula gives numbers below zero, so the tool hides it.

Neither method is a medical test. Your vet looks at weight, teeth, joints, blood work and history to judge how your dog is aging.

Dog age in human years chart

This short chart shows both methods side by side. See the full dog years chart for every age from 1 to 16.

Human years by dog age and size
Dog age	Small	Medium	Large	Giant	DNA clock
1	15	15	15	12	31
2	24	24	24	22	42
3	28	28	28	31	49
4	32	32	32	38	53
5	36	36	36	45	57
6	40	42	45	49	60
8	48	51	55	64	64
10	56	60	66	79	68
12	64	69	77	93	71
14	72	78	88	107	73
16	80	87	99	121	75

Small is 20 pounds or less, medium is 21 to 50, large is 51 to 90, and giant is over 90 pounds. Size bands follow the AVMA senior pet guide.

Why do big dogs age faster?

Large and giant dogs grow fast and reach old age sooner, so each year after adulthood counts for more. Scientists have not fully explained why. In most mammals, bigger species live longer, but within dogs the trend runs the other way.

A 2024 study in Scientific Reports looked at more than 584,000 dogs in the UK. Small breeds lived longer than large ones on average. Flat faced breeds such as the French Bulldog had some of the shortest median life spans, at 9.8 years. The Dog Aging Project is a large US study that tracks thousands of dogs to learn more about how they age.

Life stages and senior age by size

The AVMA says a dog becomes a senior in the last 25 percent of its expected life span. Using AKC data, that means:

Small or toy breeds under 20 pounds: 8 to 11 years
Medium breeds, 20 to 50 pounds: 8 to 10 years
Large breeds, 50 to 90 pounds: 8 to 9 years
Giant breeds over 90 pounds: 6 to 7 years

Senior dogs need a vet visit twice a year or more, according to the AVMA. Exams can catch problems such as arthritis, kidney disease and dental disease early.

Calculators by breed

Each breed page covers lifespan from vet studies, common health problems, senior age and an age chart.

More tools

FAQ

How old is my dog in human years?

Enter the age and adult size above. For a medium dog, year one is about 15 human years, year two adds about 9, and each year after adds about 4 to 5. A 5 year old medium dog is about 36. Large and giant dogs age faster after year five.

Is one dog year equal to 7 human years?

No. The AVMA says dogs do not age at a rate of 7 human years per dog year. Dogs grow up much faster in the first two years, then slow down. Size also matters, since big dogs reach old age sooner than small ones.

Which method is more accurate?

Neither one is exact for every dog. The size chart follows the AVMA guide and is best for comparing dogs of different sizes. The DNA clock is based on blood samples from Labrador Retrievers, so it fits medium and large dogs best. It does not adjust for size.

Why does the DNA method make young dogs so old?

The formula is a log curve. Dogs change fast at first, so a 1 year old dog has DNA marks close to a 31 year old person. A 2 year old lands near 42. After that, the curve flattens and each extra year adds less.

When is my dog a senior?

The AVMA says a dog is senior in the last 25 percent of its expected life span. Using AKC data, that is about 8 to 11 years for small dogs, 8 to 10 for medium, 8 to 9 for large and 6 to 7 for giant breeds.

How do I find the age of a rescue dog?

A vet can estimate age from the teeth, eyes, coat and joints. The estimate is usually a range of a few years in adults. Use the middle of that range in the tool, and treat the result as a rough guide.

Does this work for mixed breeds?

Yes. Pick the size class that matches your dog's adult weight. Size is the main thing both the AVMA and the AKC use to explain different aging rates, and it works the same for mixed and pure breeds.

Dog Age Calculator

Age in human years