Dog Years to Human Years: Why Multiplying by 7 Is Wrong

No, one dog year is not seven human years. In 2020 a research team compared age-related DNA changes in Labrador Retrievers and people and found a curve, not a straight line. By their formula a 1-year-old dog is about 31 in human terms, a 5-year-old about 57 and a 10-year-old about 68. The formula came from one breed, so treat it as a guide. The American Animal Hospital Association (AAHA) itself prefers to describe a dog by life stage, not by a human age.

Is one dog year really 7 human years?

The saying is old enough that the 2020 paper begins with it. Its introduction calls the idea that every year in a dog’s life equals seven human years a piece of wisdom that reflects an intuition that development and ageing happen at different rates in different species. The authors then asked whether their data fit that saying or suggested a different alignment of time. What they found was a nonlinear relationship, which a fixed multiplier cannot reproduce.

Here is their formula next to the ×7 rule:

Dog’s age	2020 formula (human years)	“×7” rule
1 year	31	7
2 years	42	14
5 years	57	35
7 years	62	49
10 years	68	70
12 years	71	84
15 years	74	105

The formula values are worked out directly from the published equation. The two lines cross at about 9½ years, which is why the rule can seem right for a middle-aged dog. At the younger ages in the table, ×7 gives a much lower number. After that point it gives a higher one: 105 for a 15-year-old, against 74 by the formula.

How was the dog age formula worked out?

The study was published in Cell Systems by Tina Wang and colleagues, from the University of California San Diego, the US National Human Genome Research Institute and other institutions. They measured DNA methylation in whole-blood samples from 104 dogs aged from 0.1 to 16 years. The paper’s summary describes the dogs as Labrador Retrievers. They compared them with published data from 320 people aged 1 to 103.

DNA methylation is a pattern of methyl groups attached to DNA at some sites and not others. The paper explains that the methylation of tens of thousands of sites changes predictably with age, which is what “epigenetic clocks” use to estimate an individual’s age.

To line the two species up, the team gave each dog the average age of the people whose methylation patterns were most similar to its own, using the five closest people. Then they did the reverse, giving each person the average age of their most similar dogs. The two analyses gave 17 ln(x) + 33 and 16 ln(x) + 30. The authors combined them into one equation:

human age = 16 × ln(dog age in years) + 31

Here ln is the natural logarithm, the “ln” key on a calculator. A logarithmic curve climbs steeply at first and then flattens. That matches the paper’s finding that dogs’ DNA changes very rapidly in early life compared with people’s. It also matches their conclusion that dogs pass through the same biological stages as people, in the same order, but at different ages.

The authors compared the curve with five milestones: infant, juvenile, adolescent, mature and senior. They report that agreement was particularly close for the infant and juvenile and the senior stages. Two examples they give:

• About 8 weeks in a dog (0.15 years) corresponds to about 9 months in a human, the infant stage when milk teeth develop in both puppies and babies.
• The paper takes 12 years as the expected lifespan of a Labrador Retriever and shows that it translates to 70, the worldwide human life expectancy it used. Other studies measure lifespan differently and report different figures, as the next sections show.

For the adolescent and mature stages the paper says the match was more approximate, with dogs’ DNA changing faster than the physiological tables predicted.

Does the dog years formula work for puppies?

Not for very young ones. The logarithm of any number below 1 is negative, so the formula reaches zero at about 7.5 weeks of age (0.144 years) and gives a negative answer before that. The study’s human comparison samples also start at age 1, and the paper’s example for a young puppy is the 8-week one above. Just above that point the curve is steep. Worked out from the formula:

Puppy’s age	Formula (human years)
3 months	about 9
6 months	about 20
9 months	about 26
1 year	31

Between 3 months and 1 year the formula climbs by more than 20 human years, so even a small error in a puppy’s age changes the answer a lot. AAHA does not convert a puppy’s age to human years at all. It defines the puppy stage by growth: birth until rapid growth ends, at about 6 to 9 months depending on breed and size. AAHA’s 2019 life stage guidelines list distemper, adenovirus-2 and parvovirus as core vaccines, so ask your vet for the vaccination plan for your puppy.

Do big dogs age faster than small dogs?

The 2020 authors are clear about the limits of their work. They used whole blood, in which the proportions of white blood cells change with age, and they state that the study focused exclusively on Labrador Retrievers. They add that breeds with widely varying lifespans could yield different age-translation functions.

Lifespan studies show that size matters. A 2020 study analysed records of 20,970 privately owned dogs at three independent primary-care veterinary hospitals in the United States and found that body size was negatively correlated with lifespan, meaning larger dogs lived shorter lives on average. Using survival analysis, it estimated the median survival time, the age by which an estimated half of the dogs had died. For all dogs it was 15.4 years. Grouped by measured weight, for dogs of 18 months and older, it was:

Size class	Weight	Median survival time
Small	under 20 lb	16.2 years
Medium	20 to 40 lb	15.9 years
Large	40 to 90 lb	14.6 years
Giant	over 90 lb	13.4 years

When the same study assigned purebred dogs to size classes by their breed’s standard weight instead, the medians were 16.4, 15.7, 14.3 and 12.0 years, so the giant-breed figure depends on how size is measured. The same study found that dogs of the “Mountain” ancestral group had median survival times 3.5 to 4.6 years shorter than other purebred groups, even after allowing for body size.

A 2022 study of UK companion dogs used a different method: life tables built from 30,563 dogs that had died between 2016 and 2020. It put life expectancy at birth at 11.23 years. In its discussion, citing earlier work, it notes that toy and small breeds have a longer life expectancy than larger dogs. The two studies measure different things, a median survival time and a life expectancy at birth, so their numbers should not be compared directly.

What life stage is my dog in?

AAHA’s 2019 Canine Life Stage Guidelines say that, rather than attempting to calculate age equivalents to humans, the task force suggests defining life stage by both age and characteristics. The guidelines divide a dog’s life into five stages:

• Puppy: birth to the end of rapid growth, about 6 to 9 months, depending on breed and size.
• Young adult: until physical and social maturity, which most dogs reach by 3 to 4 years.
• Mature adult: until the last 25% of the dog’s estimated lifespan, which depends on breed and size.
• Senior: the last 25% of estimated lifespan, through to the end of life.
• End of life: the terminal stage, which depends on the specific disease.

AAHA describes these divisions as arbitrary, and says developmental periods phase in and out gradually. Because variation increases in the later years, it does not propose ages for the mature adult and senior stages. AAHA’s 2023 senior care guidelines repeat the point: because ageing varies with species and breed, there is no specific age for senior status.

The guidelines tie advice to the stage. Young adults should have a consultation and physical exam semiannually to annually. Mature adults should have semiannual-to-annual exams and an annual minimum database. Seniors should have at least semiannual exams and a minimum database. AAHA says a minimum database in a healthy dog may include a complete blood count, a biochemical profile and a urinalysis, along with other tests. Ask your vet which suit your dog. Nutritional assessment is part of every visit, with weight, body condition and muscle condition recorded each time.

Weight is worth watching. AAHA’s guideline cites a study in Labrador Retrievers in which dogs that stayed at their ideal weight through life lived 15% longer on average, and adds that clinical experience suggests the same is likely true of other breeds. The dog calorie calculator can help you work out how much to feed. For cats, which follow a different timetable, see When is a cat a senior? Cat life stages and check-ups. This article is general education, not advice for an individual dog.

Frequently asked questions

How old is a 10-year-old dog in human years?

By the 2020 formula, about 68 human years. The formula came from Labrador Retrievers, so the answer for another breed may differ. AAHA suggests describing a dog by life stage rather than by a human age.

At what age is a dog a senior?

AAHA’s 2019 guidelines define senior as the last 25% of a dog’s estimated lifespan. Its 2023 senior care guidelines say there is no specific age for senior status, because ageing varies with species and breed. Ask your vet what lifespan to expect for your dog’s breed.

Do bigger dogs live shorter lives?

On average, yes. A 2020 study of 20,970 US dogs found that larger body size went with a shorter lifespan, from a median of 16.2 years in small dogs to 13.4 years in giant dogs. A 2022 UK study, citing earlier work, also notes that toy and small breeds have a longer life expectancy than larger dogs.

Can I use the formula for a puppy?

Not for very young puppies. The formula equals zero at about 7.5 weeks and is negative before that, and the paper’s example for a young puppy is 8 weeks. For a puppy, AAHA’s growth-based puppy stage and your vet’s plan matter more than a human-year number.

Sources

• Wang T, et al. (2020). Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome. Cell Systems 11. https://doi.org/10.1016/j.cels.2020.06.006
• Creevy KE, et al. (2019). 2019 AAHA Canine Life Stage Guidelines. J Am Anim Hosp Assoc 55:267-290. https://www.aaha.org/wp-content/uploads/globalassets/02-guidelines/canine-life-stage-2019/2019-aaha-canine-life-stage-guidelines-final.pdf
• Dhaliwal R, et al. (2023). 2023 AAHA Senior Care Guidelines for Dogs and Cats. J Am Anim Hosp Assoc 59:1-21. https://www.aaha.org/wp-content/uploads/globalassets/02-guidelines/2023-aaha-senior-care-guidelines-for-dogs-and-cats/resources/2023-aaha-senior-care-guidelines-for-dogs-and-cats.pdf
• Urfer SR, et al. (2020). Lifespan of companion dogs seen in three independent primary care veterinary clinics in the United States. Canine Med Genet 7:7. https://doi.org/10.1186/s40575-020-00086-8
• Teng KT, et al. (2022). Life tables of annual life expectancy and mortality for companion dogs in the United Kingdom. Sci Rep 12:6415. https://doi.org/10.1038/s41598-022-10341-6