How dog age is calculated
The formula is human age = 16 × ln(dog age) + 31, where ln is the natural logarithm and the dog's age is in years. Researchers worked it out by comparing age-related chemical changes to DNA, called methylation, in Labrador retrievers with the same changes in people.
Dogs age quickly early in life and more slowly later on, so the result rises steeply at first and then levels off. A 1-year-old dog comes out at 31 human years, a 2-year-old at about 42 and a 4-year-old at about 53.
Why not multiply by seven?
Multiplying by seven assumes dogs age at the same pace all their lives. It makes young dogs seem much younger than they are: a 1-year-old dog is close to its adult size, which fits 31 human years better than 7.
For older dogs the two methods are closer. A 10-year-old dog is about 68 by the formula and 70 by the seven-times rule.
Limits of the formula
The study used Labrador retrievers. Breeds of different sizes have different lifespans, so for other breeds treat the result as an estimate. The formula rises very steeply for puppies, so the calculator starts at age 1.
The result is an average for dogs of that age. It can't tell you how healthy your dog is, so talk to your vet about your dog's health as it gets older.
Inputs for the dog age calculator
Your dog's age
Enter the age in years. Decimals are fine, so 2.5 means two and a half years. The calculator covers ages from 1 to 30.
CALCULATOR QUESTIONS
Dog age calculator questions
How old is my dog in human years?
Enter its age above. As a guide, the formula gives about 31 human years at age 1, 42 at 2, 53 at 4, 64 at 8 and 71 at 12.
Is the seven-year rule wrong?
It's a rough average. It makes young dogs seem far younger than they are, and it's closer to the formula for older dogs.
Does my dog's breed or size matter?
Yes. Smaller breeds generally live longer than larger ones, and the study only included Labradors, so the result is an estimate for other breeds.
Why can't I enter an age under 1?
The formula rises very steeply in a dog's first year and gives unreliable results for young puppies, so the calculator starts at 1 year.