Dog Age Calculator: How Old Is Your Dog in Human Years?
The old seven-times rule is too simple. Dogs age fast in their first two years and then slow down, and larger dogs age faster later — this calculator follows that pattern.
What is the Dog Age Calculator?
Enter a dog's age in years and its size, and the tool estimates a human-equivalent age: the first year counts as 15 human years, the second adds 9, and each later year adds 5 for a medium dog (4 for small, 6 for large). This is a rough guide, not a veterinary assessment — breed and health matter more than any single formula.
How to use it
- Enter the dog's age in years.
- Choose the dog's size.
- Click Calculate Dog Age for the human-equivalent estimate.
Worked example
A 5-year-old medium dog works out to about 39 human years: 15 for the first year, 9 for the second, and 5 each for the next three years.
Why is the first year worth 15 human years?
Because a one-year-old dog is roughly like a human teenager in maturity, not like a seven-year-old child.
Frequently asked questions
Do large dogs age faster?
Yes, later in life. That is why large dogs add 6 per year after year two here, against 4 for small dogs.
Is this a veterinary assessment?
No. It is a rough guide. For health decisions, ask a vet who knows the dog.