Key takeaways
- The "×7" rule is a myth — dogs age fast early, then slow down.
- Year 1 ≈ 15 human years; year 2 ≈ 24; then ≈ 4–6 per year by size.
- Bigger dogs age faster in their later years than small dogs.
- A 3-year-old medium dog ≈ 29 human years.
How dog age converts to human years
A dog's age in human years isn't a straight multiple — dogs mature very quickly in their first two years and then age more gradually, at a rate that depends on body size. The widely used pattern is: the first year is about 15 human years, the second adds about 9 (reaching ~24), and each year after that adds roughly 4–6 human years, with larger breeds on the higher end.
That's why a fixed "multiply by 7" never worked — it badly overstates a young dog and understates an old small dog.
Worked example: a 3-year-old medium dog
15 (year 1) + 9 (year 2) + 5 (the third year, medium size) = 29 human years. A giant breed of the same age would be a little older (~30–31), a small breed a little younger (~28).
Dog age in human years (medium dog)
| Dog age | Human years | Life stage |
|---|---|---|
| 1 year | 15 | Adolescent |
| 2 years | 24 | Young adult |
| 3 years | 29 | Adult |
| 5 years | 39 | Adult |
| 7 years | 49 | Senior |
| 10 years | 64 | Senior |
What to do with the number
Use the life stage to guide care: seniors benefit from twice-yearly vet checks and joint support. To plan a growing puppy, pair this with the puppy weight predictor, and for cats use the cat age calculator.
Frequently asked questions
How do I calculate my dog's age in human years?
Year 1 ≈ 15, year 2 adds ≈ 9 (≈24), then ≈ 4–6 per year by size. A 3-yr medium dog ≈ 29.
Is one dog year really seven human years?
No — that's a myth. Dogs mature fast early then age slowly, so a fixed multiplier is inaccurate.
Does size affect how a dog ages?
Yes — large and giant breeds age faster in later years; small dogs age more slowly and live longer.
How old is a 3-year-old dog?
About 29 human years for a medium dog; slightly less for small, slightly more for giant.
When is a dog a senior?
Around age 7 for most dogs — earlier (5–6) for giant breeds, later (8+) for small breeds.
How accurate is this?
A solid estimate from breed-size aging patterns; individual dogs vary with genetics, weight, and health.
Aging pattern follows modern veterinary guidance — see the American Kennel Club, which reflects research that dogs age fast early then slow by size (rather than the old ×7 rule).
Last reviewed June 2026