Dog Age Calculator
Find out how old your dog or cat is in human years. It compares the old 7x rule with a size-based chart and the newer DNA-based formula.
A 5-year-old medium-sized dog:
- 7x rule: 5 × 7 = 35 human years
- Size-based chart: 15 for the first year, 9 for the second, then 5 for each of the 3 years left, which gives 15 + 9 + 15 = 39 human years
- DNA-based formula: 16 × ln(5) + 31 = 16 × 1.609 + 31 = about 57 human years
The methods disagree because they measure different things. The size-based chart is based on how big dogs mature, while the DNA method looks at chemical changes in Labrador Retrievers, which race ahead in the first few years. A cat aged 8 works out at 24 + 6 × 4 = 48 human years.
| Dog age | Small | Medium | Large | Giant |
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First year 15, second year 9, then 4, 5, 6 or 7 human years for each dog year, depending on size.
How do I convert dog years to human years?
The old rule of multiplying by seven is too crude. A more realistic guide is that the first year of a dog's life equals about 15 human years, the second year adds about 9 more, and each year after that adds 4 to 7 years depending on the size of the dog. Enter your dog's age and size in the calculator to see all three methods side by side.
Is one dog year really seven human years?
No. The 7 to 1 rule was a simple rule of thumb that fits an average life span, but dogs mature much faster than humans in their first two years and then age more slowly. A one-year-old dog is closer to a teenager than a seven-year-old child.
What is the newer dog age formula?
Researchers at the University of California San Diego compared chemical changes to the DNA of Labrador Retrievers with those in people. They found that human age is roughly 16 × the natural logarithm of the dog's age, plus 31. It is based on one breed, so use it as a guide rather than a precise figure, especially for very small or very large dogs.
Do large dogs age faster than small dogs?
Yes, on average. Large and giant breeds tend to have shorter lives and are treated as senior dogs earlier. Many vets consider a small dog to be senior at around 10, but a giant breed at 6. That is why the size-based method adds more human years per dog year as the dog gets bigger.
How do I calculate my cat's age in human years?
A cat reaches about 15 human years in its first year and about 24 by the end of its second year. After that each year adds around 4 human years. So an 8-year-old cat is roughly 48 in human terms. Switch the calculator to cat to see this and your cat's life stage.
When is my dog considered a senior?
It depends on size. As a rough guide, small dogs become seniors at about 10 years, medium dogs at 8, large dogs at 7 and giant breeds at 6. If your dog is slowing down, drinking more or losing weight, book a check with your vet whatever their age, as many problems are treatable when caught early.
Source for the DNA-based formula: Wang T. et al., Quantitative translation of dog-to-human aging by conserved remodeling of the DNA methylome, Cell Systems, 2020.