Pet Age Calculator

Choose dog or cat and enter your pet's age to see it in human years. Dogs are adjusted for size, because large breeds age faster: a 6-year-old Labrador is about 45 by the size chart, or about 60 by a 2020 DNA-based formula. The old rule that one dog year equals seven human years is wrong.

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Updated 19 October 2026

Dog

Cat

Age — years

and months

Breed

Age in human years

45 years

Using the size chart for large dogs.

Life stage: Adult — larger breeds reach their senior years sooner than small ones
DNA-based estimate: 60 years; 16 × ln(age) + 31, measured in Labradors
Size group: Large — 23 to 45 kg (50–100 lb)

Dog years to human years, large dogs
Dog age	Human years
1 year	15
2 years	24
3 years	28
4 years	32
5 years	36
6 years ◀ now	45
7 years	50
8 years	55
9 years	61
10 years	66
11 years	72
12 years	77
13 years	82
14 years	88
15 years	93
16 years	99

Please note

These are rules of thumb for comparing life stages, not a health assessment. Your vet can judge how your pet is ageing far better than any chart.

How to use the Pet Age Calculator

1Choose Dog or Cat.
2Enter your pet's age in years and months.
3For a dog, choose the breed — or choose by weight for a mixed breed.
4Read the human-equivalent age, life stage and the full chart for that size.

How it works

The old rule that one dog year equals seven human years is wrong in both directions. Dogs mature very quickly — a one-year-old dog is roughly as developed as a teenager — and then age more slowly, at a pace that depends on size.

For dogs the calculator uses the size-based chart widely used by veterinary practices: the first year counts as about 15 human years (12 for giant breeds), the second adds about 9, and each year after that adds from 4 years for small dogs to 7 for giant ones. Breeds are grouped by typical adult weight — small up to 9 kg (20 lb), medium to 23 kg (50 lb), large to 45 kg (100 lb) and giant above that — and ages between whole years are interpolated.

It also shows a newer estimate from a 2020 study by researchers at the University of California, San Diego, who compared age-related chemical marks on DNA in Labrador retrievers and people: human age ≈ 16 × ln(dog age) + 31. It was measured in one breed, so treat it as an interesting comparison rather than the answer.

For cats the calculator follows International Cat Care's chart: a cat is about 15 in human terms at one year and 24 at two, and each year after that adds about four human years.

The formula

dog: size chart DNA estimate = 16 × ln(dog age) + 31 cat = 24 + 4 × (age − 2)

ln: the natural logarithm
ages in years; the cat formula applies from two years old

The DNA-based estimate applies from one year old.

Worked example

A 6-year-old Labrador Retriever

Labradors are large dogs.
The large-dog chart gives 45 human years at age 6.
The DNA formula gives 16 × ln 6 + 31 = 59.7.

Result: About 45 in human years by the size chart, or about 60 by the DNA-based formula.

Tips and common mistakes

For a mixed-breed dog, choose by weight rather than guessing a breed.
Use the life stage to plan care: senior pets usually benefit from more frequent check-ups.
Remember the result is an estimate; health and lifestyle matter as much as age.
Compare the two dog estimates as a range rather than picking one as exact.

Frequently asked questions

Is one dog year really seven human years?

No. Dogs age fastest in their first two years and more slowly afterwards, and larger dogs age faster than smaller ones. The seven-year rule has no scientific basis.

Why do big dogs age faster?

Large and giant breeds have shorter lifespans and reach old age sooner. The biological reasons are still being studied, which is why the chart adds more human years per year for bigger dogs.

When is a cat a senior?

Feline life-stage guidelines class cats over 10 years old as seniors — about 56 in human terms.

My dog is a mixed breed. Which size do I choose?

Choose by weight: enter your dog's healthy adult weight and the calculator picks the size group.

How old is a 10-year-old cat in human years?

About 56: 24 at two years old, plus about four human years for each year after that.

How old is a one-year-old dog in human years?

About 15 for most sizes, or about 12 for giant breeds. Dogs mature very quickly in their first year.

Why do the two dog estimates disagree?

They come from different methods. The size chart is the traditional veterinary guide; the DNA-based formula comes from a study of Labrador retrievers. Together they give a sensible range.

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