Dog Years to Human Years
The ×7 rule is a fable. A 2-year-old Great Dane is a senior; a 2-year-old Chihuahua is a teenager. Size drives the curve.
Bake these anchors into your head: year 1 ≈ 15 human years. Year 2 ≈ +9 (so 24). After year 2, each dog-year adds 4 (giant) / 5 (large) / 6 (medium) / 7 (toy). The AVMA/Kirby cosign curve; big dogs age faster after the start, which is why the myth dies.
How the math works
- Anchors (AVMA table): yr 1 = 15, yr 2 = 24. After that, +4/yr (giant), +5 (large), +6 (medium), +7 (toy), the divergence is the biology: large breeds age faster in mid-life, toy breeds decelerate.
- 2019 Nature (Keller/Fedrizzi epigenetic methylation) supports the shape: dogs burn through their "startup" human years fast, then the per-year cost drops (puppy's first year ≈ a human's two decades).
- Senior thresholds (AKC consensus): giant 5–6 yr, large 6–7, medium 7–8, toy 9–10. Life-stage row uses these.
- Lifespan baselines: giant ~10 yr, large ~11, medium ~13, toy ~15, % row is against these averages.
How old is a 3 year old dog in human years?
~31 for a medium dog, ~28 for a giant, ~34 for a toy. The ×7 myth says 21 for all three, which is exactly why the myth died: a 3-year-old Great Dane is not a 21-year-old human.
Why do big dogs age faster?
The 2019 epigenetic clock study showed fast early methylation (puppy year 1 ≈ human 30), and large-breed dogs pay a steeper per-year cost across mid-life, in exchange for the skeletal growth that shortens them. Small breeds invert both.
At what age is my dog senior?
By class: giant 5–6, large 6–7, medium 7–8, toy 9–10. Senior = the year geriatric bloodwork and joint management start, not the year people start saying "he's old."