Age in dog years
The first dog year is worth about fifteen human years and the second about nine. After that each year adds four to seven depending on size; four for a small dog, seven and a half for a giant breed.
How to convert to dog years
Size is the dominant variable and it works the opposite way to most mammals. Across species, larger animals generally live longer. An elephant outlives a mouse by decades. Within dogs the relationship inverts: a Great Dane rarely reaches nine while a small terrier commonly passes fifteen. The reason is not settled, though rapid growth and higher rates of age-related disease in large breeds are the leading explanations.
Questions
No. The first is about fifteen, the second nine, then four to seven by size.
Large breeds age faster and die younger; the opposite of the usual pattern across species.
About 34 in human terms for a medium dog, 39 for a giant breed.
A 2020 formula from DNA methylation: 16 × ln(age) + 31. It fits the biology better but behaves oddly under a year.
Small ones. Many toy breeds reach fifteen or more; giant breeds often do not reach nine.