Dog Age Calculator
Convert your dog's age into human years — adjusted for breed size, because a 10-year-old Chihuahua and a 10-year-old Great Dane are nowhere near the same age.
Size changes the answer a lot. Not sure of the breed? Pick the mixed-breed option closest to their adult size.
Human-age equivalents are a well-established approximation, not a measurement, and lifespan figures are averages for the size class with very wide individual variation. Neither predicts anything about your own dog — ask your vet about their health.
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Why one dog year is not seven human years
The ×7 rule appears to have come from a rough observation that people lived to about 70 and dogs to about 10. It has no scientific basis, and it is wrong in a way that matters: it badly understates how fast a puppy grows up and badly overstates how fast an older small dog ages.
A dog reaches sexual maturity and close to full size inside its first year. Developmentally that is not a seven-year-old child — it is much nearer a 15-year-old. Ageing is front-loaded: enormous in year one, still fast in year two, then steady.
The second thing the rule misses is size. Among dogs, bigger means shorter-lived — unusual in mammals, and still not fully explained, though faster growth and earlier onset of age-related disease are both implicated. A giant breed is a senior at six. A toy breed is barely middle-aged at the same point.
How this calculator works
It uses the size-adjusted veterinary approach rather than a single multiplier:
- Year one is worth about 15 human years, spread unevenly — a three-month puppy is around 4, a six-month puppy around 10.
- Year two adds roughly 9 more, putting a two-year-old dog near 24.
- Every year after adds a fixed amount set by size: about 4 for small and toy breeds, 4.5 for medium, 5.25 for large and 6.75 for giant.
Because your dog's breed already tells us its size class, you do not have to guess which bucket it belongs in.
You know the numbers. Now watch the trend.
A single weigh-in tells you very little — a chart of the last six months tells you everything. PetNoter keeps your dog's weight history in one place, free.
- Log a weigh-in in seconds and see the trend line
- Reminders for weigh-ins, vaccinations and vet visits
- Vet records, prescriptions and photos stored per pet
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Dog age chart: dog years to human years
Human-year equivalents by age and size. Small is under 9 kg (20 lbs), medium 9–23 kg (20–50 lbs), large 23–45 kg (50–100 lbs), and giant over 45 kg (100 lbs).
| Dog's age | Small | Medium | Large | Giant |
|---|---|---|---|---|
| 1 year | 15 | 15 | 15 | 15 |
| 2 years | 24 | 24 | 24 | 24 |
| 3 years | 28 | 28.5 | 29.3 | 30.8 |
| 4 years | 32 | 33 | 34.5 | 37.5 |
| 5 years | 36 | 37.5 | 39.8 | 44.3 |
| 6 years | 40 | 42 | 45 | 51 |
| 7 years | 44 | 46.5 | 50.3 | 57.8 |
| 8 years | 48 | 51 | 55.5 | 64.5 |
| 9 years | 52 | 55.5 | 60.8 | 71.3 |
| 10 years | 56 | 60 | 66 | 78 |
| 11 years | 60 | 64.5 | 71.3 | 84.8 |
| 12 years | 64 | 69 | 76.5 | 91.5 |
| 13 years | 68 | 73.5 | 81.8 | 98.3 |
| 14 years | 72 | 78 | 87 | 105 |
| 15 years | 76 | 82.5 | 92.3 | 111.8 |
| 16 years | 80 | 87 | 97.5 | 118.5 |
| 18 years | 88 | 96 | 108 | 132 |
| 20 years | 96 | 105 | 118.5 | 145.5 |
Life stages, and what changes at each
The number is less useful than the stage it puts your dog in. These boundaries shift with size — bigger dogs reach every one of them sooner.
| Size | Senior from | Typical lifespan |
|---|---|---|
| Toy & small | 10 years | 12–16 years |
| Medium | 8 years | 11–14 years |
| Large | 7 years | 10–12 years |
| Giant | 6 years | 8–10 years |
Lifespan figures are averages across a size class, and individual variation is very wide — plenty of dogs live well beyond them. They are here to show when senior care becomes worth starting, not to predict anything about your own dog.
Frequently Asked Questions
Is one dog year really seven human years?
No. The 'multiply by seven' rule has no scientific basis and is misleading at both ends. A one-year-old dog is sexually mature and near its adult size, which is closer to a 15-year-old human than a seven-year-old child. Ageing then slows down, but how fast it slows depends on the dog's size.
How do you calculate a dog's age in human years?
The first year of a dog's life is worth about 15 human years, the second adds about 9 more (roughly 24 by the second birthday), and every year after that adds between 4 and 7 human years depending on size. Small breeds add about 4 per year, medium about 4.5, large about 5.25 and giant breeds about 6.75.
Why does size change the answer?
Large and giant breeds age faster than small ones — one of the few cases in mammals where bigger means shorter-lived. A 10-year-old small dog works out at roughly 56 in human years, while a 10-year-old giant breed is closer to 78. Any calculator that ignores size gives the same answer for a Chihuahua and a Great Dane, which is the main thing wrong with most of them.
When is a dog considered a senior?
It depends on size rather than a fixed number. Giant breeds are generally considered senior from about 6 years, large breeds from 7, medium breeds from 8, and small and toy breeds from around 10. Senior dogs are usually recommended twice-yearly check-ups instead of annual ones.
What about the DNA study that gave a different formula?
A 2020 study from UC San Diego measured DNA methylation and produced the formula 16 × ln(dog age) + 31. It is a genuinely interesting piece of research, but it was derived from Labrador Retrievers alone, it takes no account of size, and it behaves poorly for puppies. This calculator uses the size-adjusted veterinary approach instead, which matches how dogs actually age across breeds.
How accurate is a dog age calculator?
It is a well-established approximation, not a measurement. Individual dogs vary enormously with genetics, weight, diet and veterinary care, and mixed breeds fall between the size categories. Use it as a guide to what life stage your dog is in rather than as a precise number.
More free tools
Track your dog's weight in the free PetNoter app
4.8 · Free · Android & iOS