How do you convert dog years to human years?

The first year of a dog's life counts as about 15 human years and the second adds about 9 more, reaching 24. After that each dog year adds roughly 4 to 7 human years depending on size, with smaller dogs ageing more slowly and giant breeds fastest. This calculator follows that breed-size model rather than a flat multiplier.

Why is the "multiply by seven" rule wrong?

The old rule that one dog year equals seven human years assumes ageing is steady, but pets grow up far faster in their first two years and then level off. Multiplying by seven understates a puppy's early development and misreads an older pet's stage, so vets use the modern curve instead, which is what this tool applies.

How do cat years compare to human years?

Cats follow a similar early curve: the first year is about 15 human years and the second reaches 24. From there each cat year adds about 4 human years, so a cat of 10 works out to roughly 56. Cats do not use size bands, since the range in body size is much smaller than in dogs.

Does dog size really change the result?

Yes. Small and toy breeds tend to live longer and age more slowly in later life, while large and giant breeds age faster, so the same age in years maps to a higher human age for a big dog. That is why the calculator asks for a size band once you pick dog.

Pet Age Calculator

Convert your dog or cat years to human years the modern way. Pick the species, enter the pet's age in years and months, and for dogs choose a size band, then read the human-years equivalent. This uses the breed-size ageing model rather than the debunked "multiply by seven" rule, so the answer reflects how pets really age. Free and instant in your browser.

Convert your dog or cat's age into human years the way vets now do it. Pick the species, enter the age in years and months, and for dogs choose a size band, then read the human-years equivalent and life stage. It uses the breed-size ageing curve instead of the old times-seven rule, so it answers how old is my dog in human years more honestly.

Leap-year accurate
100% free
No sign-up, no app
Instant as you type
Works offline after first load

Read the guide: Dog Years to Human Years, Explained

Size

Age in yearsAge in months

In human years

🐶 about 29

Your dog is 3 years old, so in their prime.

Pet age

3 years

Human years

29 yrs

Species

Dog

Size band

Medium

Method: the first year counts as about 15 human years and the second adds about 9 more, reaching 24. After that each year adds 4 to 7 human years depending on size, following the modern breed-size model rather than the old "multiply by seven" rule.

How to use it

1
Choose dog or cat

Select the species. Dogs and cats age on slightly different curves, so this changes the result.
2
Enter the age and size

Type the age in years and months. For dogs, pick a size band, because bigger dogs age faster.
3
Read the human years

See the human-years equivalent, the life stage, and a friendly line you can copy and share.

When it comes in handy

Understanding life stage

See whether your pet is a youngster, in their prime or a treasured senior, so care can match their age.

Vet visits and diet

Get a sense of where your pet sits in human terms when planning check-ups, food or exercise.

Fun and sharing

Find out your pet's "human age" and share the result line with family and friends.

Instant, accurate & 100% in your browser

The calculation runs right here in your browser, counting the real calendar so leap years and month lengths come out right. Nothing you type is sent to a server, there is no sign-up and no limit, and once the page has loaded it keeps working even with no connection.

Frequently asked questions

How do you convert dog years to human years?: The first year of a dog's life counts as about 15 human years and the second adds about 9 more, reaching 24. After that each dog year adds roughly 4 to 7 human years depending on size, with smaller dogs ageing more slowly and giant breeds fastest. This calculator follows that breed-size model rather than a flat multiplier.
Why is the "multiply by seven" rule wrong?: The old rule that one dog year equals seven human years assumes ageing is steady, but pets grow up far faster in their first two years and then level off. Multiplying by seven understates a puppy's early development and misreads an older pet's stage, so vets use the modern curve instead, which is what this tool applies.
How do cat years compare to human years?: Cats follow a similar early curve: the first year is about 15 human years and the second reaches 24. From there each cat year adds about 4 human years, so a cat of 10 works out to roughly 56. Cats do not use size bands, since the range in body size is much smaller than in dogs.
Does dog size really change the result?: Yes. Small and toy breeds tend to live longer and age more slowly in later life, while large and giant breeds age faster, so the same age in years maps to a higher human age for a big dog. That is why the calculator asks for a size band once you pick dog.

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How to use it

Choose dog or cat

Enter the age and size

Read the human years