Set your dog's age and size above to see their human age equivalent.
How Old Is My Dog in Human Years?
A dog's first year equals about 15 human years and the second adds about 9, so a 2-year-old dog is roughly 24 in human years. After that each year adds about 4 to 5 human years for small and medium dogs, and more for large and giant breeds. Pick your dog's age and size above for a size-adjusted estimate.
Two Ways to Convert Dog Years
The veterinary rule of thumb
The American Veterinary Medical Association's commonly cited guide: year one = 15 human years, year two = about 9 more (24 in total), then about 4 to 5 human years per dog year. Big dogs age faster after that, so this calculator uses a size-adjusted chart: after age 6 a giant breed adds roughly 7 to 8 human years a year, a small breed about 4.
The DNA methylation formula
In 2020 a UC San Diego team (Wang and colleagues, published in Cell Systems) compared chemical marks on the DNA of 104 Labrador Retrievers with the same marks in humans. Their fit was human age = 16 × ln(dog age) + 31. For a 4-year-old dog: ln(4) = 1.386, times 16 is 22.2, plus 31 gives about 53. The formula ages young dogs very fast (a 1-year-old is 31) and then slows sharply. It was built on one breed only, and it goes negative for puppies younger than about 7 weeks, so treat it as a research curve rather than a rule.
Dog Age in Human Years: Comparison Chart
Size columns come from the chart this calculator uses; the last column is the Cell Systems formula, rounded.
| Dog age | Small (under 20 lb) | Medium (21 to 50 lb) | Large (51 to 90 lb) | Giant (over 90 lb) | 16 ln(age) + 31 |
|---|---|---|---|---|---|
| 1 | 15 | 15 | 15 | 15 | 31 |
| 2 | 24 | 24 | 24 | 24 | 42 |
| 3 | 28 | 28 | 28 | 28 | 49 |
| 4 | 32 | 32 | 32 | 32 | 53 |
| 5 | 36 | 36 | 36 | 36 | 57 |
| 6 | 40 | 42 | 45 | 49 | 60 |
| 7 | 44 | 47 | 50 | 56 | 62 |
| 8 | 48 | 51 | 55 | 64 | 64 |
| 10 | 56 | 61 | 66 | 79 | 68 |
| 12 | 64 | 70 | 77 | 93 | 71 |
| 14 | 72 | 78 | 88 | 108 | 73 |
| 16 | 80 | 87 | 99 | 123 | 75 |
The two methods agree roughly around age 8 and disagree most for young dogs and old giant breeds. Neither is a medical measurement; both are ways to picture where your dog is in its life.
When Is a Dog a Senior?
The American Animal Hospital Association's canine life stage guidelines (2019) do not use a fixed birthday. They define the senior stage as the last 25% of a dog's expected lifespan. Using the average lifespans this calculator shows for each size, that works out to roughly:
- Small (about 15 years expected): senior from about 11
- Medium (about 13 years): senior from about 10
- Large (about 11 years): senior from about 8
- Giant (about 9 years): senior from about 7
Your own dog's breed, weight and health history matter more than any chart, so ask your vet when to start senior checkups and bloodwork.