How to use the Pet Age Calculator (Dog and Cat Years)
- Choose dog or cat.
- Enter your pet’s age in years. Use decimals for half years, such as 2.5.
- Read the equivalent human age and the result of the old seven-year rule.
Formula used
Dogs: human age = 16 × ln(dog age) + 31 (a 2019 study of DNA ageing in Labradors). Cats: 15 years for the first year, 24 for the second, then 4 more for each year after.
Worked example
Here is the Pet Age Calculator (Dog and Cat Years) worked through with the example values shown above, so you can check each step by hand.
| Inputs | |
|---|---|
| Pet | Dog |
| Pet’s age | 5 years |
| Result | |
| Equivalent human age | 57 |
| Old "multiply by 7" rule | 35 |
| Method used | Dog: 16 × ln(age) + 31 |
The dog formula
For dogs the calculator uses human age = 16 × ln(dog age) + 31, a formula from a 2019 study that compared chemical changes in the DNA of ageing Labrador retrievers with those in people. A 5-year-old dog works out to about 57 human years, against 35 by the seven-year rule. A 1-year-old dog is about 31, and a 10-year-old about 68.
The curve climbs steeply early and flattens later, which matches how dogs develop: a one-year-old dog is roughly a mature teenager, and each later year adds less.
The cat rule
For cats the usual convention is 15 human years for the first year, 24 for the second, and 4 more for every year after that. A 1-year-old cat is 15, a 2-year-old is 24, and a 10-year-old is 56.
The cat rule is a convention, not a precise measurement, but it matches how fast cats reach adulthood and the life stages that vets describe.
Why size and breed matter
Large dogs tend to age faster and live shorter lives than small ones, so a Great Dane at 7 may be further along than a Chihuahua at 7. The dog formula was built on Labradors, a medium-to-large breed, so treat it as a middle estimate.
Indoor cats on average live longer than outdoor cats. Health, diet and care all change how a pet ages.
Using the number
The human-age figure is helpful for thinking about life stage: when a pet is a young adult, middle-aged or senior. Vets often move pets to senior diets and check-ups from around age 7 for dogs and 10 for cats, depending on size and breed.
It is not medical advice. Ask your vet when your pet needs more frequent check-ups.
Frequently asked questions
Is one dog year really seven human years?
No. It is a rough average. Dogs age faster early on and slower later.
Where does the dog formula come from?
A 2019 study of DNA changes in Labradors suggested human age = 16 × ln(age) + 31.
How old is a 1-year-old cat?
About 15 in human terms by the common rule.
Does breed matter?
Yes. Large breeds usually age faster than small ones.
Can I enter a puppy’s age in months?
Use decimals, for example 0.5 for six months. The minimum is 0.5 years.
When is a pet a senior?
Around 7 years for dogs and 10 for cats, but it varies. Ask your vet.
This calculator gives estimates for information only. Actual figures from a bank, employer, tax authority or doctor may differ. It is not financial, tax, legal or medical advice.