Dog Age Calculator
Convert dog years to human years using two methods: the classic size-based chart and the newer epigenetic formula from a UC San Diego study (human age = 16 ln(dog age) + 31). Example: a 7-year-old medium dog is about 49 by the chart and about 62 by the formula.
Show steps
How to use the Dog Age Calculator
- Enter your dog’s age in years (use decimals, such as 2.5).
- Choose the size group that matches your dog’s adult weight.
- Press Calculate to see the human-year equivalent by both methods.
Formula and method
Classic chart: the first dog year equals 15 human years, the second adds 9, and every year after adds 4, 5, 6 or 7 for small, medium, large and giant dogs. The epigenetic method from a 2020 UC San Diego study estimates human age = 16 x ln(dog age) + 31.
Worked example: a 7-year-old medium dog
| Method | Calculation | Human age |
|---|---|---|
| Classic chart | 15 + 9 + 5 x 5 | 49 |
| Epigenetic formula | 16 x ln(7) + 31 | 62 |
Dog years to human years by size (classic chart)
| Dog age | Small | Medium | Large | Giant |
|---|---|---|---|---|
| 1 | 15 | 15 | 15 | 15 |
| 2 | 24 | 24 | 24 | 24 |
| 3 | 28 | 29 | 30 | 31 |
| 5 | 36 | 39 | 42 | 45 |
| 7 | 44 | 49 | 54 | 59 |
| 10 | 56 | 64 | 72 | 80 |
| 12 | 64 | 74 | 84 | 94 |
| 15 | 76 | 89 | 102 | 115 |
Why the old 7-to-1 rule is wrong
Multiplying dog years by seven treats a one-year-old dog as seven, but a dog is sexually mature by about one year. Dogs age quickly in the first two years and more slowly afterward, and larger breeds age faster than small ones, which is why a size-based chart or an epigenetic formula is closer to reality.
Frequently asked questions
How do I calculate my dog’s age in human years?
Use the size chart: 15 for year one, 9 for year two, then 4 to 7 per year depending on size. Or use 16 x ln(age) + 31.
Is one dog year really seven human years?
No. That is a rough rule that does not match how dogs age.
Do small dogs live longer?
Generally yes. Small breeds often live 12 to 16 years, while giant breeds average 7 to 10.
When is a dog a senior?
Around age 7 for most dogs, earlier for giant breeds and later for small breeds.
Why does the formula use a logarithm?
Dogs age fast when young and then slow down, which matches a logarithmic curve based on changes in DNA methylation.
Does breed matter?
Yes. The formula was based on Labrador Retrievers, and other breeds can age differently. Ask your vet about your dog’s breed and health.
Sources
- Wang et al. 2020, Cell Systems: Quantitative translation of dog-to-human aging
- AVMA: Dog life stages and care
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