Pet Age Calculator
Convert your dog or cat's literal age into equivalent human years based on size and breed.
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Pet age to human years
Equivalent human age
39 human years
5-year-old medium dog · Life stage: Mature adult
Keep an eye on weight and dental health as your dog approaches the senior years.
The 7-year rule is a myth
The old “1 dog year equals 7 human years” rule is inaccurate. Pets age very rapidly in their first two years — reaching the equivalent of a human in their mid-twenties — and then the pace slows to about 4–7 human years per calendar year depending on size.
Smaller dogs live significantly longer than larger breeds, which is why a Great Dane is considered “senior” at age 6 while a Chihuahua might not be until about 10.
How to use the Pet Age calculator
Choose dog or cat, then enter your pet’s age in years and months. For dogs, pick the size that matches their adult weight — size matters because large and giant breeds age faster after their second birthday.
The calculator shows the equivalent human age and which life stage your pet is in, with a quick care tip. Add your pet’s name if you’d like a shareable card (“Max is 52 in human years”), and copy the link to send the exact result to someone else.
For mixed breeds, use the size your dog is (or is expected to be) when fully grown.
Formula
First year = 15 human years. Second year = +9 (so a 2-year-old is about 24).
Each year after that: small dogs +4, medium +5, large +6, giant +7, cats +4.
Human age = 24 + (pet age − 2) × yearly rate. Ages under two are scaled proportionally.
Frequently asked questions
How old is my dog in human years?
A one-year-old dog is roughly 15 in human years and a two-year-old about 24. After that, add about 4 years per year for small dogs, 5 for medium, 6 for large and 7 for giant breeds. So a 7-year-old medium dog is about 49 and a 7-year-old giant dog about 59.
Is one dog year really seven human years?
No. The 7-to-1 rule is a myth. Dogs mature very quickly in their first two years — a one-year-old dog is closer to a 15-year-old teenager — and then age more slowly. How fast they age after that depends mostly on size.
How old is my cat in human years?
A one-year-old cat is about 15 in human years and a two-year-old about 24. After that, each cat year is roughly 4 human years, so a 10-year-old cat is around 56 and a 15-year-old cat about 76.
Why do large dogs age faster than small dogs?
Large and giant breeds grow quickly and tend to develop age-related conditions earlier, so they have shorter average lifespans. A Great Dane may be considered senior at 6, while a Chihuahua may not be senior until about 10.
When is a dog or cat considered a senior?
Vets often define senior as the last quarter of expected lifespan. For dogs that is roughly 10+ for small breeds, 8+ for medium, 7+ for large and 6+ for giant breeds. Cats are usually considered senior from around 11 years old.
How accurate is a pet age calculator?
It gives a good rule-of-thumb comparison, not a medical measurement. Genetics, breed, diet, weight and healthcare all affect how a pet ages. Your vet can give the best picture of your pet’s health for their age.