Dog years explained

By Dexaloop · Updated 27 October 2026 · Checked against the sources listed below

One dog year is not seven human years. A medium-sized dog is about 15 in human terms at age one, about 24 at two, and then ages roughly 4 to 5 human years for each dog year. That pattern comes from the American Veterinary Medical Association (AVMA) guideline quoted by the American Kennel Club (AKC). Size changes the later years: small dogs age more slowly and giant dogs faster. A newer formula from a 2020 UC San Diego study, based on changes in DNA, gives yet another answer: human age = 16 ln(dog age) + 31. This guide explains why the old rule fails, how each method works, and how to use them sensibly.

Why "times 7" is wrong

The x7 rule assumes dogs age at the same speed all their lives. They do not. The AKC states it directly: "Contrary to popular belief, dogs do not age at a rate of 7 human years for each year in dog years."

The problem is clearest at the two ends of life. For a 1-year-old dog, x7 gives 7, while the vets' chart below gives 15. For a 16-year-old medium dog, x7 gives 112, older than almost any person, while the chart gives 87. A straight multiplier is too slow early and too fast later.

The vets' rule of thumb: 15, then 9, then about 5

The AKC quotes the AVMA guideline for a medium-sized dog:

• "15 human years equals the first year of a medium-sized dog's life."
• "Year two for a dog equals about nine years for a human."
• After that, each dog year is "approximately five years" for a human.

The AVMA's own chart, below, follows this pattern. Its footnote says it is "Based on a medium-sized dog weighing 21-50lbs."

The DNA column is worked out from the formula in the next section and rounded to whole years.

Why size matters

The AVMA chart covers one size only, a medium dog. The AKC publishes a chart that compares equivalent ages by dog weight, and its article lists among its key points that "Size and breed significantly impact lifespan and aging rate." Its FAQ adds that different breeds age at different rates, "which is why any age conversion is only an estimate."

The AKC explains the reason: "Smaller breeds generally have longer life spans and tend to age more slowly than larger dogs." It quotes the AVMA that larger breeds "tend to have shorter lifespans compared to smaller breeds." So a 10-year-old Chihuahua and a 10-year-old Great Dane are at very different stages of life, even though both are 10.

Because the chart is organized by weight, a puppy or a mixed breed is placed by how heavy it will be once fully grown. A breed name alone can mislead, since dogs of one breed vary.

The 2020 DNA formula

In 2020 a team led from UC San Diego published a different approach in the journal Cell Systems. Instead of matching life milestones, they compared methylation, chemical tags on DNA that change in a regular way as an animal ages, in dogs and in people. The study used "104 Labrador retrievers spanning a 16-year age range," with dogs from 0.1 to 16 years old at the time of the blood draw. (The university's press release gives 105 dogs; the paper's figure is used here.)

The result was a single formula:

human_age = 16 ln(dog_age) + 31

The dog's age goes in as years, including fractions, and ln means the natural logarithm (base e), not the log button most calculators show first. Spreadsheet users can type =16*LN(7)+31 for a 7-year-old dog.

Worked example

1. Dog's age: 7 years.
2. Natural log of 7: 1.946.
3. 16 x 1.946 = 31.13.
4. 31.13 + 31 = 62.1, so about 62 in human years.

For a 3-month-old puppy, the age is 0.25 years and ln(0.25) is negative (about -1.386), so the answer is 16 x -1.386 + 31 = 8.8. A logarithm climbs fastest near zero, so the formula races through the puppy months and then flattens out, which matches how quickly young dogs mature.

How far to trust it

The formula is a fitted curve, not a law of nature, and it comes with clear limits:

• It was built from one breed. The paper says "Distinct breeds exhibiting widely varying lifespans" could "yield different age-translation functions."
• The university release notes it "was developed using a single breed of dog."
• The AKC adds that because "the study included just a single breed, your own dog's 'human age' based on this formula may not quite match up."

So the DNA formula and the vets' chart answer slightly different questions. The chart matches stages of life, such as when a dog counts as senior. The formula matches biological markers. Neither is exact for an individual dog.

Which number should you use?

• For everyday comparisons, such as explaining to a child how old the dog is, the AKC size chart is the most practical.
• For curiosity about the science, the DNA formula is interesting, especially for young dogs.
• For health decisions, ask your vet. The AVMA chart itself says pet ages are approximate and to ask your veterinarian.

Common mistakes

• Multiplying by 7. It understates young dogs and overstates old ones.
• Ignoring size. A Chihuahua and a Great Dane of the same age are at different life stages.
• Using log base 10 instead of the natural log. On a calculator, use the ln key, not log.
• Treating the DNA formula as breed-proof. It came from Labradors only.
• Using a puppy's current weight. A growing dog belongs in the column for its grown-up size.

The calculator below applies the AKC size chart, shows the DNA formula's figure alongside it, and works from years and months or a date of birth.

Questions

Sources

• American Kennel Club: How to calculate dog years to human years
• American Veterinary Medical Association: Pets age faster than people (chart, PDF)
• Wang et al., Quantitative translation of dog-to-human aging by conserved remodeling of the DNA methylome, Cell Systems 11(2), 2020 (PubMed Central author manuscript)
• UC San Diego Today: How old is your dog in human years? (2 July 2020)

This guide is general information, not legal, tax or financial advice. Rules change; check the official source for your own case. Found a mistake? Email support@dexaloop.com.

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