Is one dog year really seven human years?

No — that rule is folklore and gets young dogs badly wrong. A dog's first year is closer to fifteen human years and its second adds about nine more, after which the rate settles somewhere between four and seven per year depending on size.

Why does a dog's size change how fast it ages?

Larger breeds mature at a similar rate but decline faster afterwards, with shorter average lifespans. A Great Dane is often considered senior around six years old, while a small terrier is not until about ten.

How do cat years compare to dog years?

Cats follow the same fast start — about fifteen human years for the first year and nine for the second — but then age more slowly and consistently at roughly four human years per year, with no size adjustment.

What is the DNA-methylation dog age formula?

It is human age equals 16 times the natural logarithm of the dog's age, plus 31, published in 2020 from a comparison of chemical ageing markers in dog and human genomes. It captures the steep early curve but ignores breed size.

Can the Pet Age Calculator tell me if my pet is healthy?

No. It converts ages using population averages and life-stage conventions. Health depends on breed, weight, diet and individual history, which is a conversation for a vet.

Pet Age Calculator

Convert dog and cat years into human years using a size-adjusted ageing curve rather than the old multiply-by-seven rule.

The Pet Age Calculator runs entirely in your browser. Your pet's age and size are used only for the conversion on your device and are never uploaded.

Open the Age Calculator

About Pet Age Calculator

Pet Age Calculator replaces the multiply-by-seven folklore with the curve animals actually follow. Dogs and cats mature very fast and then slow down: the first year is worth roughly fifteen human years, the second adds another nine, and every year after that adds between four and seven depending on how big the animal is. Size is a real input rather than a cosmetic one, because larger dogs age faster once mature — a giant breed is considered senior at six while a small terrier is not until ten. For dogs, a second estimate from the 2020 DNA-methylation study is shown alongside the table, and an ageing curve lists the equivalents across a full lifespan.

Features

Separate curves for dogs and cats rather than one shared rule
Four dog size bands with different post-maturity ageing rates
Partial years pro-rated, so a six-month puppy is handled properly
Life-stage label from puppy or kitten through to senior
DNA-methylation estimate shown alongside the table for dogs
Ageing curve table across a full lifespan
Reverse direction: convert a human age into pet years
Everything computed on your device

How to use the Pet Age Calculator

Choose dog or cat
Enter your pet's age in years — decimals are fine for young animals
For a dog, pick the size band that matches its adult weight
Read the human-equivalent age, life stage and current ageing rate

Example

Input

5-year-old medium dog

Output

39 human years · adult · ageing 5 human years per year

Fifteen for the first year, nine for the second, then five per year for a medium breed.

Common errors & troubleshooting

The result is very different from the old seven-times rule. — It should be. Multiplying by seven puts a one-year-old dog at seven human years, which is nowhere near right — a one-year-old dog is physically closer to a fifteen-year-old human.
Two dogs the same age show different human ages. — That is the size effect. After maturity, a giant breed adds about seven human years per year against a small breed's four, which is why large dogs reach senior status several years earlier.
The DNA-methylation figure disagrees with the table. — They are two different models. The table is the size-adjusted veterinary convention; the formula comes from a study of chemical ageing markers and does not account for breed size at all, so they diverge most at the extremes.
No estimate shows for a cat. — The DNA-methylation formula was derived from dogs, so it is deliberately not applied to cats. The staged table still gives the cat equivalent.

Frequently asked questions

Is one dog year really seven human years?: No — that rule is folklore and gets young dogs badly wrong. A dog's first year is closer to fifteen human years and its second adds about nine more, after which the rate settles somewhere between four and seven per year depending on size.
Why does a dog's size change how fast it ages?: Larger breeds mature at a similar rate but decline faster afterwards, with shorter average lifespans. A Great Dane is often considered senior around six years old, while a small terrier is not until about ten.
How do cat years compare to dog years?: Cats follow the same fast start — about fifteen human years for the first year and nine for the second — but then age more slowly and consistently at roughly four human years per year, with no size adjustment.
What is the DNA-methylation dog age formula?: It is human age equals 16 times the natural logarithm of the dog's age, plus 31, published in 2020 from a comparison of chemical ageing markers in dog and human genomes. It captures the steep early curve but ignores breed size.
Can the Pet Age Calculator tell me if my pet is healthy?: No. It converts ages using population averages and life-stage conventions. Health depends on breed, weight, diet and individual history, which is a conversation for a vet.

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