BYTETOOLS

Dog Age Calculator

Convert dog years to human years with the epigenetic clock formula and the size-band table side by side, plus the reverse and a cat conversion.

Human equivalent age

34 human years

A 4.0-year-old dog in the medium size band works out at 34.0 human years on the size-band table, or 53.2 on the epigenetic clock. Life stage: Mature adult.

4.0 yr
Dog age
34.0 yr
Size-band equivalent
53.2 yr
Epigenetic clock
Mature adult
Life stage

Age conversion table

Dog ageSize-band tableEpigenetic clock
6 months7.519.9
1 yr15.031.0
2 yr24.042.1
3 yr29.048.6
4 yr34.053.2
5 yr39.056.8
6 yr44.059.7
7 yr49.062.1
8 yr54.064.3
10 yr64.067.8
12 yr74.070.8
14 yr84.073.2
16 yr94.075.4

The size-band column uses 15 human years for the first year, +9 for the second, then +5 per year for the medium band. The clock column is 16 × ln(age) + 31.

Why the two columns disagree

The 2020 epigenetic study compared DNA methylation in Labrador retrievers with the same marks in humans and fitted human age = 16 × ln(dog age) + 31. It puts a one-year-old dog at about 31 and a four-year-old at about 53, then flattens out sharply — by 14 it is only at 73. The familiar size-band table is a veterinary rule of thumb built from life expectancy instead, so it rises in a straight line and pulls ahead at the older end.

Neither is “the” answer. The clock was fitted on one breed and describes molecular ageing; the size-band table captures the very real fact that a Great Dane is old at eight while a chihuahua is barely middle-aged. Reading them side by side is more useful than picking one.

A fun estimate, not veterinary advice. Individual breeds, health history and care vary enormously, and the epigenetic formula is undefined at birth and unreliable for very young puppies, so it is only shown from about three months. Ask your vet about anything to do with your animal’s health. All calculations run in your browser.

What is the Dog Age Calculator?

The 2020 epigenetic clock puts a dog's human-equivalent age at 16 × ln(dog age) + 31, so a one-year-old dog is about 31 and a four-year-old about 53. The older size-band rule counts the first year as 15, the second as 9 more, then 4–7 per year depending on size.

  • Epigenetic clock (16 × ln age + 31) and size-band table side by side
  • Small, medium, large and giant bands with a weight-based suggestion
  • Reverse conversion from human years back to pet years
  • Cat mode using the standard 15 / +9 / +4 feline progression
  • Life-stage label from puppy or kitten through to senior
  • Full conversion table from six months to sixteen years

How to use the Dog Age Calculator

  1. 1

    Choose dog or cat, and whether you are converting pet years to human years or the other way around.

  2. 2

    Enter your pet's age in years and months, or the human age you want converted back.

  3. 3

    For dogs, pick a size band — or enter an adult weight and let the calculator suggest one.

  4. 4

    Compare the size-band and epigenetic-clock figures in the result tiles.

  5. 5

    Scan the conversion table to see how the two methods diverge as your dog gets older.

About the Dog Age Calculator

The ByteTools Dog Age Calculator shows two answers rather than one, because there genuinely are two. The first is the epigenetic clock from a 2020 study that compared DNA methylation patterns in dogs and humans and fitted human age = 16 × ln(dog age) + 31. It rises steeply early and then flattens, which is why a one-year-old dog already sits around 31.

The second is the familiar veterinary size-band table: 15 human years for the first year, another 9 for the second, then between 4 and 7 more per year depending on whether your dog is small, medium, large or giant. Enter an adult weight and the tool will suggest the right band. There is a reverse conversion for turning a human age back into dog years, and a cat mode using the standard feline progression of 15, then 24, then about 4 a year.

Everything is calculated in your browser. This is a fun estimate, not veterinary advice — breed, health history and care matter far more than any formula.

Frequently asked questions

How do you convert dog years to human years?

The modern research-based answer is 16 × the natural log of your dog's age, plus 31 — so a two-year-old dog is about 42 and a ten-year-old about 68. The older rule of thumb counts the first year as 15 human years, the second as another 9, and every year after that as 4 to 7 depending on the dog's size.

Is one dog year really seven human years?

No — that was never more than a rough average and it is wrong at both ends. A one-year-old dog is closer to a human teenager or young adult than to a seven-year-old child, and the ageing rate slows markedly later in life rather than staying constant.

Why do big dogs age faster than small dogs?

Large and giant breeds have shorter life expectancies and reach their senior years earlier — a Great Dane is often considered senior by five or six, while a small terrier may not be until eight or nine. The size-band table builds this in by adding more human years per dog year as size increases.

What is the epigenetic clock formula for dogs?

Human age = 16 × ln(dog age) + 31, from a 2020 study that compared DNA methylation in Labrador retrievers against human methylation data. It was fitted on one breed, so treat it as a well-grounded estimate rather than a universal law.

Why do the two methods give different answers?

They measure different things. The clock describes molecular ageing and flattens out sharply, while the size-band table is derived from life expectancy and rises in a straight line. They agree reasonably in early adulthood and diverge for older dogs, which is why both are shown.

How do cat years convert to human years?

The standard feline life-stage guidance treats the first year as about 15 human years and the second as 9 more, reaching 24, then adds roughly 4 for every year after that. A ten-year-old cat is therefore around 56 in human terms.

Related tools