Dog Age Calculator
Convert dog years to human years by breed size (and see why multiplying by seven is wrong).
Your dog
How old is your dog?
That is a medium dog, 21–50 lb: beagles, border collies, bulldogs
Multiplying by seven is the most repeated pet fact there is, and it is wrong at both ends: it makes a one-year-old dog a seven-year-old child, when it is closer to a teenager. Use age to decide when senior check-ups start (around seven for large breeds, later for small ones) and ask your vet rather than a chart.
This converts your dog's age into human years. Enter the age and weight, and it returns the human-year equivalent along with the life stage your dog is in: puppy, young adult, mature, senior or geriatric.
You can compare two methods: the AVMA guideline that adjusts for body size, and the 2020 DNA-based formula from genetics research. They disagree, which is itself worth seeing.
How old is a dog in human years?
Dogs do not age at a steady rate, and they do not age seven times faster than us. The multiply-by-seven rule is a myth, most likely a 1950s marketing simplification that stuck.
The real pattern is front-loaded. A dog's first year takes it from newborn to fully grown and sexually mature, which is roughly 15 human years of development. The second year adds about nine more. Only after that does ageing settle into a steadier pace.
Size then takes over, which is the main way dogs differ from cats. A small terrier can reach 16; a great dane rarely sees 10. So after year two, a large dog ages faster in human terms than a small one, which is why weight matters here and a single chart cannot be right for every dog.
Multiplying by 7 would make a one-year-old dog 7 in human terms. In reality it is a fully grown adult, closer to 15. That is where the old rule fails worst.
What to enter
- Years and months
- Your dog's actual age. Months matter a lot for puppies, where a few weeks is a large share of their life so far.
- Weight
- Used to work out the size band, because big dogs age faster after the first two years. Weight is asked for rather than 'small/medium/large' because you know what your dog weighs, but whether a 55 lb boxer counts as medium is exactly the guess worth removing.
- Method
- AVMA is the veterinary guideline and adjusts for size. Epigenetic is the 2020 research formula based on DNA, which is more scientific but ignores breed entirely.
The two methods, and why they disagree
- AVMA / AKC guideline
- 15 human years for the first year, 9 for the second, then 4 to 5.5 a year depending on size. What most vets use. Adjusts for the fact that large breeds age faster.
- Epigenetic (Wang et al., 2020)
- human age = 16 × ln(dog age) + 31, from comparing DNA methylation in dogs and humans. It makes a 1-year-old dog 31 in human terms, far older than the chart methods.
- Why they differ
- The DNA study used only Labrador Retrievers, so it cannot account for breed size. It is the only method with a molecular basis rather than a chart, but it is one breed's clock applied to all dogs.
- The old ×7 rule
- No scientific basis. It gets puppies badly wrong in one direction and giant breeds badly wrong in the other.
What this assumes
The dog is reasonably healthy and of typical build for its weight. Illness and obesity both shorten lifespan.
Mixed breeds are estimated from weight, which is the best available proxy when the breed mix is unknown.
How to calculate your dog's age in human years
The veterinary method is three simple steps, and you can do it in your head.
- 24
- The first two years: 15 then 9
- rate
- About 4 for a small dog, 4.5 medium, 5.5 large
First year counts as 15. A one-year-old dog is roughly a 15-year-old human: fully grown, just reaching adulthood.
Second year adds 9. So a two-year-old dog is about 24 in human terms, whatever its size.
Then add per year by size. Roughly 4 a year for a small dog, 4.5 for a medium one, 5.5 for a large one.
See a worked example: a 10-year-old dog, small versus large
- Age
- 10 years
- Compare
- a small breed against a large one
First two years are 24 for both.
That leaves 8 more years to count.
Small dog at 4 a year: 24 + (8 × 4) = 56 human years.
Large dog at 5.5 a year: 24 + (8 × 5.5) = 68 human years.
Same age, twelve human years apart. The DNA method gives 67.8 for both, since it cannot tell them apart.
56 human years if small, 68 if large
Frequently asked questions
No. There is no scientific basis for it, and it is thought to have come from 1950s marketing as an easy round number.
It fails worst at both ends. A one-year-old dog is not a 7-year-old child; it is fully grown and able to breed, closer to 15. And a giant breed at 10 is far older than 70 in human terms.
About 24, on the veterinary guideline. The first year counts as roughly 15 and the second adds about 9.
Size barely matters yet at this point, because the size difference only starts compounding from year three onwards.
Roughly 4 human years, since the first year is worth about 15 and three months is a quarter of it.
That matches what you see: a three-month-old puppy is a toddler. Walking and playing confidently, learning fast, and with no judgement whatsoever.
Because larger dogs age faster after the first two years and have shorter lives. A small terrier commonly reaches 15 or 16; a great dane rarely reaches 10.
So a 10-year-old small dog works out at about 56 in human terms, while a 10-year-old large dog is nearer 68. The reason large breeds age faster is still an open research question.
For everyday purposes use the AVMA result, because it accounts for size and matches what vets use for life-stage care.
The epigenetic figure is worth seeing because it has real science behind it, but it was built from Labrador Retrievers alone, so it applies one breed's ageing clock to every dog.
Usually around 8 years for a medium dog, but it comes earlier for large breeds and later for small ones. Some giant breeds are considered senior by 6.
It matters practically: many vets move to twice-yearly check-ups at that point, because catching things early is what extends good years.
Problems people actually run into
Using ×7 to decide when a dog is old
The rule makes a 7-year-old dog seem middle-aged at 49, which is roughly right for a small breed and badly wrong for a large one already entering its senior years.
That matters more than trivia. Senior screening, diet changes and joint care are all pegged to life stage, so the wrong mental model delays them.
Assuming a mixed breed ages like its biggest parent
Adult weight predicts ageing better than breed guesswork does, which is why this calculator asks for pounds rather than a breed name.
For a rescue of unknown parentage, weigh the dog and use that. It is a better input than a DNA-test guess at the breed mix.
Results are estimates for general information only and are not professional financial, medical, or legal advice. Read our full disclaimer.
Sources
- Calculating your dog's age · UC Davis School of Veterinary Medicine
- How old is your dog in human years? Scientists develop better method than 'multiply by 7' · University of California San Diego
Last updated: September 3, 2026