A better formula than ×7
Dogs do not age at a constant rate. They mature explosively in their first two years and then settle into a slower, size-dependent pace. This calculator models that:
year 1 → 15 human years
year 2 → +9 (total ≈ 24)
each later year → +4 (small) / +5 (medium) / +6 (large)
So a dog's human age is built up in stages rather than multiplied by a single number. Small breeds add the fewest human years per dog year because they live longest; giant breeds add the most.
Worked example
A 5-year-old medium breed:
First 2 years: 15 + 9 = 24 human years.
Remaining 3 years: 3 × 5 = 15.
Human age: 24 + 15 = 39 years.
Why it varies: the same 5-year-old as a large breed would be 24 + (3 × 6) = 42, while a small breed would be 24 + (3 × 4) = 36. Size is the single biggest factor in canine aging.
How accurate is this?
No formula is exact — aging depends on genetics, weight, diet and care. The staged, size-adjusted approach used here reflects veterinary consensus far better than the discredited ×7 myth, and lines up reasonably with the epigenetic "DNA clock" research published in recent years.