What is my dog's age in human years?

There's no single figure: the curve is fast early on, then slows. A 5-year-old dog sits roughly around 40 human years, but a giant breed will be 'older' than a small one at the same actual age.

Is the 7-year rule true?

No. It's a popular but mistaken shortcut: a dog ages fast in his first two years, then much more slowly. The epigenetic clock from Wang et al. (2020) confirms a logarithmic curve, not a fixed multiplier.

What number do you multiply a dog's age by?

By no single number, that's exactly the point. The first year weighs ~15 years, the second ~9, the following ones ~4 to 5: the 'factor' shrinks with age. Any fixed multiplier (the ×7 first and foremost) gets it wrong.

How do you estimate the age of a rescue dog whose birth date is unknown?

That's the vet's job: they estimate age by looking at the teeth (wear, tartar), the eyes, the coat and overall condition. It's only a range, but it's enough to set up the right monitoring and diet.

Working out my dog's age

Caring for my ageing dogPart of · Caring for my ageing dog

Working out my dog's age

Q: How do you work out a dog's age?

Count roughly 15 human years for the first year, +9 for the second (about 24 years at age 2), then 4 to 5 years for each additional year. Adjust for size: a big dog ages faster than a small one.

Q: At what age is a dog a senior?

It depends mainly on his size: a large or giant breed is senior from 6-7 years , a small dog more like 9-10 years . Vets place it in the last quarter of estimated life expectancy (AAHA markers).

6 min read

Forget the ×7 rule: it's wrong. A dog ages fast at first, then slowly. To estimate his age in human years: count about 15 years for his first year, +9 for the second (so around 24 at the age of 2), then 4 to 5 years for each year after that. And the bigger he is, the faster he ages.

Why the seven-year rule doesn't hold up

A dog doesn't age at a steady pace. He grows and matures at full speed over his first two years, then the rhythm settles down. The dog-age / human-age curve isn't a straight line: it climbs quickly, then it slows. That's what a 2020 American study confirmed by comparing the ageing of dog and human DNA. Multiplying by 7 ignores that reality, and it's mainly past the first couple of years that the sum goes wrong.

Estimating his age in human years

You don't need a complicated formula: four markers, the ones used by the American veterinary association (AVMA), are enough to give you a good idea.

The first year counts for about 15 human years

A puppy grows and matures at full tilt: at 1 year old, his body is already that of a young adult.

The second year adds about 9 years

At 2, your dog is somewhere around 24 in human years. The pace is already starting to slow.

Each year after that is worth about 4 to 5 years

After the age of 2, ageing slows down markedly. This is where the "×7" gets it most wrong.

Adjust for size

A big dog ages faster than a small one: shift your estimate upwards for a giant breed, downwards for a small dog.

For the curious: this 2020 American study measures a dog's age from chemical marks that build up on his DNA over time. It draws out a formula that traces the same curve, fast at first then slower and slower. As it was built on Labradors, its figures don't line up with the "15 years for the first year" marker: remember the shape of the curve, not a number to apply to the letter.

Size changes everything

Adult size is what matters most. Small dogs live longer and age slowly; large and giant breeds age faster and don't live as long. A large 2022 British study of 876,000 dogs puts average life expectancy at around 11 years, with a wide spread depending on size and breed.

The word "senior" doesn't arrive at the same age for every size of dog.

Small dogs (up to about 15 kg)

Senior at around 9-10 yearsThey grow more slowly than large dogs.

The longest life expectancyPlenty go past 13-14 years in good health.

Medium dogs (about 15-40 kg)

Senior at around 8 yearsThey age more slowly than large dogs, and faster than small ones.

Large and giant breeds (over about 40 kg)

Senior from 6-7 yearsThey grow fast, age fast and often don't live as long.

These ages are markers, not fixed dates: your vet will fine-tune them for your dog's breed and actual condition.

What "senior" actually means

Vets place the start of the "senior" stage in the last quarter of estimated life expectancy. That's the marker set by the American Animal Hospital Association (AAHA) in 2019 and confirmed in 2023. In practice, a dog who lives around 12 years becomes senior at about 9; a giant breed who lives around 8 becomes senior at about 6. "Senior" doesn't mean "ill": it's a signal to keep a slightly closer eye, not a diagnosis.

Wang et al. — Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome, Cell Systems (2020)
Teng et al. — Life tables of annual life expectancy and mortality for companion dogs (Scientific Reports, VetCompass data) (2022)
Canine Life Stage Guidelines, AAHA (2019)
Senior Care Guidelines, AAHA (2023)

Going further

guideRecognising the signs of ageing in my dogBeyond the sums, the real everyday clues that your dog is getting older.Read the guide guideVeterinary care for your senior dogWhy two vet visits a year change everything once your dog reaches his senior years.Read the guide guideAdapting daily life for an ageing dogSimple adjustments at home to make this new stage of life a gentle one.Read the guide guideAssessing your dog's quality of lifeA practical framework to judge whether your senior dog is doing well, beyond the numbers.Read the guide guideCognitive decline (senility) in the senior dogConfusion and disorientation: understanding age-related cognitive decline.Read the guide guideArthritis and mobility: keeping my dog comfortableStiffness and joint pain: a common problem as the years go by.Read the guide

Frequently asked questions

How do you work out a dog's age?

Count about 15 human years for the first year, +9 for the second (so around 24 at the age of 2), then 4 to 5 years for each extra year. Adjust for size: a big dog ages faster than a small one.

How old is my dog in human years?

There's no single figure: the curve is fast at first, then slows. A 5-year-old dog is roughly around 37 in human years (24 at 2 years old, then 4 to 5 per year), but a giant breed will be "older" than a small one at the same real age.

Is the seven-year rule true?

No. It's a popular belief, but a false one: a dog ages fast over his first two years, then far more slowly. A 2020 American study on dog DNA confirms it: the curve climbs quickly, then slows, so it isn't a fixed multiplication.

What do you multiply a dog's age by?

By no single figure, precisely. The first year counts for about 15 years, the second for about 9, the following ones for about 4 to 5: the factor drops with age. Any fixed multiplier, starting with ×7, gets it wrong.

At what age is a dog a senior?

It mostly depends on size: a large or giant dog is senior from 6-7 years, a small dog more like 9-10 years. Vets place it in the last quarter of estimated life expectancy (AAHA markers).

How do you estimate the age of an adopted dog whose birth date is unknown?

That's the vet's job: they estimate age by looking at the teeth (wear, tartar), the eyes, the coat and general condition. It's only a range, but it's enough to set up the right health care and diet.

Updated on July 11, 2026Sources

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