About Whiskerclock

How old is your pet, really?

Why this exists

Almost everyone has heard that one dog year equals seven human years. It's a tidy rule, it's easy to remember, and it's wrong. It was never based on research — the most common explanation is that someone in the mid-twentieth century divided average human lifespan by average dog lifespan and the number stuck.

The reality is more interesting. Dogs and cats do not age at a constant rate. They age enormously fast in their first year, quickly in their second, and then far more slowly for the rest of their lives. A one-year-old dog is not a seven-year-old child; developmentally it is closer to a teenager. Whiskerclock exists to give you a number that reflects that curve instead of flattening it.

Where the numbers come from

For dogs we show two numbers, because no single one is honest on its own. The headline follows the size-banded approach vets use: 15 human years for the first year, 9 more for the second, then between 4 and 7 a year depending on the dog's size. Underneath it we show a figure from a 2020 study at the University of California, San Diego, which compared DNA methylation — chemical marks that accumulate on DNA with age — in dogs and humans.

That study is better evidence than any rule of thumb, but it profiled 104 Labrador Retrievers, a single breed, so it cannot account for size at all. Rather than pick one and hide the other, we show both and tell you where they disagree. There are year-by-year charts for each size if you want the full table.

For cats, we use the staged approach that veterinary bodies broadly agree on: roughly 15 human years for the first year, about 9 more for the second, and approximately 4 per year after that.

The exact formulas are published in full on the calculator page. We would rather show our working than ask you to trust a black box.

How accurate is it?

Honestly: it is a well-grounded estimate, not a diagnosis. Every formula of this kind describes a population average, and your pet is an individual. Size is accounted for — a Great Dane and a Chihuahua age at genuinely different rates, and by eight years old they are in quite different stages of life — but the size adjustment itself is a veterinary convention rather than a research finding, which is why the study figure sits beside it. Breed within a size band, and health, still move the real number and we do not model them.

How the site is built

Whiskerclock is a deliberately small, fast, static website. There are no accounts, no tracking of what you enter, and no database — the calculation runs entirely in your browser. Our privacy policy explains the details, including how advertising cookies work.

Get in touch

Corrections, suggestions, and pet photos are all welcome at hello@whiskerclock.com.