Enter your dog’s age and size to convert it to human years. The old “multiply by 7” rule is wrong: dogs grow up fast in their first two years, and after that small dogs age more slowly than big ones. This calculator uses the size-based chart published by the American Kennel Club, and also shows the estimate from the 2020 epigenetic-clock study.
Don’t know the exact age? A rough estimate still works.
Pick a breed below and this sets itself.
Sets the size class and the typical lifespan.
An estimate for healthy dogs, not a health assessment. Ageing varies between individual dogs, and your vet can tell you what your dog’s stage means for care.
How old is my dog in human years?
There is no single formula that fits every dog, because dogs of different sizes age at different speeds. What vets and the American Kennel Club use instead is a chart that treats the first two years separately, then adds a different number of human years per dog year depending on how big the dog is.
The pattern behind the chart is simple:
- Year one is huge. A one-year-old dog counts as about 15 human years: physically grown, not mentally grown up. Giant breeds are the exception, counted at 12, because they are still growing at that point.
- Year two adds about nine more. A two-year-old dog lands at 24 in human terms (22 for a giant breed).
- After that, size sets the pace. On the AKC chart, each further year adds about 4 human years for a small dog, 4 to 5 for a medium one, 5 to 6 for a large one, and about 7 for a giant breed.
That last point is the part the “multiply by 7” rule gets badly wrong. A 10-year-old Chihuahua and a 10-year-old Great Dane are not the same age in any meaningful sense: the Dane is far older.
Dog age chart in human years
Table values are the American Kennel Club’s size-based chart.
| Dog age | Small | Medium | Large | Giant |
|---|
Why big dogs age faster
It is one of the odd facts of biology. Across species, bigger animals usually live longer: an elephant outlives a mouse. Within a single species, dogs included, it runs the other way. Large breeds grow much faster as puppies, reach old age sooner, and have shorter lifespans than small breeds. Researchers think the rapid early growth is part of the reason, though the mechanism is still debated.
What it means for you is practical: a giant breed is a senior years before a terrier of the same age, and should start senior-focused vet checks earlier.
The science: what the epigenetic clock says
In 2020 researchers compared chemical marks on dog and human DNA (a process called methylation) and produced the first formula for dog-to-human age based on biology rather than observation. Their result was human age = 16 × ln(dog age) + 31.
The calculator shows this as a second estimate, because it is worth knowing but it has real limits. It was built from Labrador Retrievers only, it does not account for size, and it gives strange results for very young puppies. For everyday use, the size-based chart is the better guide.
Life stages: puppy, adult, senior
Age in human years is a nice way to picture your dog, but what matters at the vet is the life stage. These are the stages used in the American Animal Hospital Association’s canine life stage guidelines.
| Stage | When | What it means for care |
|---|
How to estimate the age of a dog you adopted
If you do not know a rescue dog’s birthday, a vet can give a reasonable estimate. The clues they use:
- Teeth. The most useful clue in young dogs. Puppy teeth come in by about 8 weeks and are replaced by adult teeth by around 7 months. After that, tartar build-up and wear give a rough guide.
- Eyes. A cloudy blue-grey haze in the lens (lenticular sclerosis) is common from middle age onward.
- Muzzle. Grey hairs around the muzzle and eyebrows often start in middle age, though some dogs grey early.
- Muscle and movement. Older dogs often lose muscle over the hips and shoulders, and stiffen after rest.
Where these numbers come from
Everything in the calculator is taken from published sources, not invented for this page:
- The age chart is the American Kennel Club’s size-based chart, How to Calculate Dog Years to Human Years, using its size bands of 20 lb or less, 21 to 50 lb, 51 to 100 lb, and over 100 lb.
- Lifespan ranges come from the AKC’s How Long Do Dogs Live?: 10 to 15 years for small breeds, 10 to 13 medium, 8 to 12 large, 8 to 10 giant.
- Life stages follow the 2019 AAHA Canine Life Stage Guidelines, which define senior as the last 25 percent of expected lifespan.
- The DNA estimate is from Wang et al., Quantitative Translation of Dog-to-Human Aging (Cell Systems, 2020), based on methylation data from 104 Labrador Retrievers aged 0 to 16.