This dog age calculator converts dog years into human-equivalent years using a size-aware model instead of the old ×7 rule.
Biology
Dog Age Calculator
Estimate human-equivalent age from a dog's age and size.
Calculator
About this calculator
Formula notes
The first dog year ≈ 15 human years, the second ≈ +9, and each later year adds about 4–7 depending on size — smaller dogs age slower after maturity.
Worked examples
- Example: a 5-year-old medium dog is about 36 human years old, matching the page default.
- A 10-year-old large dog maps to a substantially later life stage than a 10-year-old small dog, so changing only the size band produces a different human-age estimate.
How to use it
- Enter your dog's age in years.
- Select the adult size: small, medium, or large.
- Read the human-equivalent age.
Frequently asked questions
Why is the ×7 rule wrong?
Dogs mature much faster in the first two years, so a flat multiplier misstates both young and old ages.
Why does size change the result?
Large breeds age faster after maturity and have shorter average lifespans than small breeds.
Limits and interpretation
- The model groups dogs by broad adult size and cannot represent every breed or mixed-breed ageing pattern.
- Human-age equivalence describes a life-stage analogy; it does not predict remaining lifespan or diagnose age-related disease.