How to use
- Choose dog or cat.
- Enter the age in years and months; for dogs, choose the size.
- Read the human-year equivalent and open the chart to compare sizes.
Options explained
- Dogs
- The first year ≈ 15 human years, the second ≈ 9 more, then 4–7 a year depending on size (the common chart cited by the AVMA).
- Cats
- Per the AAHA/AAFP Feline Life Stage Guidelines — 1 year ≈ 15, 2 years ≈ 24, then about 4 a year.
How the human-year figure is worked out
For dogs the first year counts as 15 human years (scaled in proportion for part of a year) and the second year adds 9, so a 2-year-old is 24 for every size. After that, each year adds an amount that depends on the size you choose:
| Size | Each year from 3 to 5 | Each year from 6 |
|---|---|---|
| Small (≤ 9 kg) | 4 | 4 |
| Medium (10–23 kg) | 4 | 5 |
| Large (23–41 kg) | 4 | 5.5 |
| Giant (over 41 kg) | 4.5 | 7 |
Cats follow the same 15 and 24 for the first two years and then add 4 a year. The result is rounded to a whole number, and months count as a fraction of a year. A 10-year-old medium dog is 24 + 4 × 3 + 5 × 5 = 61.
The DNA-methylation formula, 16 × ln(age) + 31, is shown for dogs of 1 year and older only. Side by side:
| Age | Small | Medium | Large | Giant | Cat | DNA formula (dog) |
|---|---|---|---|---|---|---|
| 3 | 28 | 28 | 28 | 29 | 28 | 49 |
| 5 | 36 | 36 | 36 | 38 | 36 | 57 |
| 8 | 48 | 51 | 53 | 59 | 48 | 64 |
| 10 | 56 | 61 | 64 | 73 | 56 | 68 |
| 12 | 64 | 71 | 75 | 87 | 64 | 71 |
Frequently asked questions
Isn't it just "multiply by 7"?
No. Dogs and cats mature very fast in the first year and age more slowly after that, at different rates by size.
What is the DNA-methylation formula?
UC San Diego researchers proposed 16 × ln(age) + 31 in 2020 from DNA methylation in Labradors. It gives different results from the usual chart.
How accurate is it?
It's a rough estimate. For your pet's health, ask a vet.
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