Dog years calculator
The rule seems to have originated from a rough comparison of average lifespans — about 70 years for a human and 10 for a dog. It fails at both ends. A one-year-old dog is sexually mature and physically adult, which no seven-year-old child is. And a Great Dane at seven is genuinely elderly while a Chihuahua at seven is middle-aged. Size is the dominant variable and the naive rule ignores it entirely.
The first dog year counts for about 15 human years, the second for nine, and each year after that for four to seven depending on size. A five-year-old medium dog is about 39 in human terms — not 35 as the times-seven rule suggests.
How to convert dog years
A 2020 study using DNA methylation — the epigenetic clock — produced a very different curve, 16 × ln(dog age) + 31, which ages dogs extremely fast early and then slows dramatically. It matches the biology better than any linear rule but gives odd results below one year. Both estimates are shown here because neither is definitive, and the honest summary is that dogs age fast at first, then at a rate that depends heavily on their size.
Questions
No. The first year is about 15, the second about nine, and later years four to seven depending on size.