Pet Age Calculator
Find out how old your dog or cat is in human years.
Note: Human-year figures are a model, not a clinical reading. Both methods here estimate from age alone and cannot see your pet's breed mix, weight, or health. Use them as a guide and ask your veterinarian for advice specific to your pet.
Dog age by size, side by side
The same dog year lands on a different human age depending on size, because bigger dogs age faster once they mature. Tap a size to open its full chart.
| Dog age | Small | Medium | Large | Giant | UCSD formula |
|---|---|---|---|---|---|
| 1 year | 15 | 15 | 15 | 12 | 31 |
| 2 years | 24 | 24 | 24 | 22 | 42 |
| 3 years | 28 | 28 | 28 | 31 | 49 |
| 5 years | 36 | 36 | 36 | 45 | 57 |
| 8 years | 48 | 51 | 55 | 64 | 64 |
| 10 years | 56 | 60 | 66 | 79 | 68 |
| 13 years | 68 | 74 | 82 | 100 | 72 |
| 16 years | 80 | 87 | 99 | 121 | 75 |
Values are human years. The UCSD column applies to dogs and is based on Labrador data.
How this calculator works
The first result reads from a size adjusted chart, the kind veterinary sources use: a dog's first year counts for about 15 human years, the second adds roughly nine more, and each year after that adds four to seven depending on size. Cats follow their own curve. It lines up well with how a pet looks and behaves at a given age.
The second result, shown for dogs, comes from the 2020 UCSD formula, human age equals sixteen times the natural log of the dog's age plus thirty one. Researchers built it from DNA methylation, so it tracks biological aging rather than a flat ratio. It reads high for young dogs and flattens later, which is why its number can differ from the chart. Neither is the single truth. The chart mirrors everyday veterinary practice, the formula reflects one rigorous study of Labradors, and the old idea of multiplying by seven matches neither. Both estimate from age alone, so breed, weight, lifestyle, and illness still shift the real picture. For the full method and sources, see our methodology and editorial policy.
Sources
- Wang, T. and colleagues (2020). Quantitative translation of dog-to-human aging by conserved remodeling of the DNA methylome. Cell Systems.
- American Association of Feline Practitioners and AAHA, life stage guidelines, for cat and dog stage thresholds.
- Veterinary consensus on size adjusted dog aging and average lifespan by size.
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Frequently Asked Questions
Why does the calculator ask for my dog's size?
Because size changes how fast a dog ages. Small dogs live longest and age gently after their first two years, while large and giant breeds age faster and reach their senior years sooner. This calculator applies a size-based curve rather than one flat rate, so the result fits your dog's build.
How do you calculate a dog's age in human years?
Dog age calculation depends on size. Small dogs: first year = 15 human years, second = 9, then 4 per year. Large dogs age faster, with giant breeds aging approximately 7-8 human years for each dog year after maturity.
Do cats age the same as dogs?
Cats follow a different aging pattern. A 1-year-old cat is roughly 15 in human years, a 2-year-old is about 24, and after that cats age approximately 4 human years for each cat year.