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.
- Bigger dogs age faster in their later years.
- A 3-year-old medium dog ≈ 29 human years.
Why "times seven" never worked
The old rule assumed a dog ages at a steady 7 human years per calendar year. But dogs don't age evenly: they hit puberty within the first year and are physically mature by two, then age much more gradually. A 1-year-old dog is closer to a 15-year-old human than a 7-year-old, and an old small dog is younger than ×7 would suggest.
The modern formula
The dog age calculator applies this with a size adjustment automatically — just enter the age and pick a size.
Size changes everything after age two
Small dogs live longest and age slowly in later life; giant breeds age fastest. That's why size is the key input once a dog is past two years old.
| Dog age | Small | Medium | Giant |
|---|---|---|---|
| 2 years | 24 | 24 | 24 |
| 5 years | 36 | 39 | 44 |
| 10 years | 56 | 64 | 76 |
What to do with the number
Use it to spot when your dog becomes a senior (around 7, earlier for giant breeds) and to time twice-yearly vet visits and joint care. Raising a puppy? Pair this with the puppy weight predictor; for cats, use the cat age calculator.
Frequently asked questions
Is one dog year seven human years?
No — that's a myth. Dogs mature fast early (year 1 ≈ 15) then age slowly, so a single multiplier is wrong.
How do I calculate my dog's age?
Year 1 ≈ 15, year 2 adds ≈ 9 (≈24), then ≈ 4–6 per year by size.
Why do bigger dogs age faster?
Large/giant breeds have shorter lifespans and gain more human-equivalent years per year after age two.