“One dog year equals seven human years” is one of the most repeated — and least accurate — rules of thumb around. Our pet age calculator uses better formulas for both dogs and cats.
Why the ×7 rule is wrong
Dogs mature far faster than humans in their first couple of years, then age more slowly afterward. A flat multiplier can’t capture that curve — a 1-year-old dog isn’t “7 human years old” in any meaningful developmental sense, and a 12-year-old dog isn’t simply “84.”
The dog formula
We use a formula derived from a 2020 UC San Diego study that compared DNA methylation patterns (“epigenetic clocks”) between dogs and humans:
Human age = 16 × ln(dog age) + 31This logarithmic curve matches the rapid early aging and the slower later aging that real dogs show. A 5-year-old dog comes out to about 56.8 human years — not 35.
The cat formula
Common veterinary aging charts use a tiered approach instead: roughly 15 human years for a cat’s first year, another 9 for the second year (24 total by age 2), then about 4 more human years for every year after that. A 5-year-old cat works out to about 36 human years.
What it doesn’t account for
Breed and size matter in real life — larger dog breeds age faster and have shorter lifespans than smaller breeds — but this calculator gives a general-purpose estimate that applies reasonably well across typical breeds rather than a breed-specific number.