In more detail
A 2020 study by Wang and colleagues (Cell Systems), which compared DNA methylation in Labrador retrievers and humans, proposed human age ≈ 16 × ln(dog age) + 31. Its curve shows what the old "times seven" rule hides: dogs age very fast in the first two years and more slowly afterwards. Veterinary rules of thumb have a similar shape: the first year of a medium-sized dog is about 15 human years, the second adds about 9, and each later year adds roughly 4 to 5, more for large breeds.
Why it matters
Life stage drives care: senior check-ups, diet and screening start earlier for large and giant breeds, which age faster and usually live shorter lives than small dogs. The methylation formula was derived from a single breed and is not meant for puppies under about a year, so treat any conversion as a rough guide and ask a vet about an individual dog.
Example
Dog age 16 × ln(age) + 31 Old rule (× 7)
1 31.0 7
2 42.1 14
5 56.8 35
10 67.8 70
14 73.2 98