How to use the Dog Age
- Enter your dog's age in years and months.
- Select the size category by adult weight.
- Read the human-equivalent age.
- Use the life-stage note to guide veterinary check-up frequency.
How the calculation works
A dog's first year corresponds to roughly 15 human years across all sizes, and the second adds about nine more, putting a two-year-old dog near 24. After that the rate diverges by size: small breeds under 10 kg add about four human years annually, medium breeds about five, large breeds six, and giant breeds seven or more. A seven-year-old Great Dane is geriatric while a seven-year-old Chihuahua is barely middle-aged.
The reason large dogs age faster is still debated, but rapid early growth and higher lifetime cell division are the leading explanations, with cancer incidence rising accordingly. An epigenetic clock based on DNA methylation gives a smoother curve — 16 × ln(dog age) + 31 — which tracks the biology better than any linear rule. Practically, most vets recommend twice-yearly examinations once a dog enters its senior stage, which arrives at around six for giant breeds and ten for small ones.
Year 1 ≈ 15, year 2 ≈ +9, then +4 to +7 per year by size ; epigenetic: 16 × ln(age) + 31Source: AVMA size-adjusted dog age guidance and the Wang et al. (2020) epigenetic clock for dogs.
Worked example
A 9-year-old Labrador weighing 32 kg (large breed).
- First two years = 24 human years.
- Remaining 7 years × 6 = 42.
- Total = 66 human years.
- Epigenetic estimate: 16 × ln(9) + 31 = 66.2.
About 66 human years — firmly senior, warranting twice-yearly veterinary checks.
Frequently asked questions
Is one dog year really seven human years?+
No. It badly overstates year one and understates ageing in large breeds later.
Why do large dogs age faster?+
Rapid growth and higher lifetime cell turnover are the leading explanations, along with higher cancer rates.
When is a dog considered senior?+
Around six for giant breeds, seven or eight for large, and ten for small breeds.
Does neutering affect lifespan?+
Evidence suggests a modest increase on average, largely by removing certain cancer and infection risks.
Last reviewed August 31, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.