Dog Age Calculator
Convert a dog’s age into approximate human years based on the dog’s size, and compare the common size-based chart with a newer DNA-based formula.
How dog years are calculated
The old rule of 7 human years per dog year is too simple. Dogs mature quickly in their first two years, and larger breeds age faster after that. The size-based rule used here is:
- Year 1 = about 15 human years.
- Year 2 = about 9 more (24 total).
- Each year after: about 4 (small), 5 (medium), 6 (large) or 7 (giant) human years.
Worked example
A 5-year-old medium dog: 24 + 3 × 5 = 39 human years.
DNA-based formula
Human age ≈ 16 × ln(dog age) + 31
This formula comes from a 2020 study of DNA changes in Labrador retrievers. It suggests dogs age very fast early on: a 5-year-old dog comes out at about 57.
Frequently asked questions
Is one dog year really seven human years?
No. That rule ignores the fast early growth and the differences between breeds and sizes.
How old is a 10-year-old dog in human years?
Roughly 56 for a small dog, 64 for a medium dog and 72 for a large dog using the size chart.
Why do large dogs age faster?
Larger breeds tend to have shorter lifespans and show age-related changes earlier.
When is a dog considered a senior?
Many vets consider small dogs senior at around 10 and large dogs at around 6 to 8.
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