Dog age in human years

In 2020, researchers at the US National Human Genome Research Institute, the University of California San Diego and other universities measured DNA methylation in the blood of 104 dogs, mostly Labrador Retrievers, aged from 0.1 to 16 years. DNA methylation is a chemical change to DNA that shifts with age in dogs and in people. They compared it with published data from 320 people aged 1 to 103 and found that dog age and human age line up on a curve, not a straight line. Their combined formula is:

human age = 16 × ln(dog age in years) + 31

ln is the natural logarithm, the “ln” key on a calculator. At 1 year the formula gives 31. At 2 years it gives 42. The authors’ own check was that the expected lifespan of a Labrador, 12 years, comes out at about 71, close to the 70 they used for worldwide human life expectancy. They also found that dogs’ DNA changes much faster in early life than people’s does.

The paper actually fitted the curve both ways round (dog to human, and human to dog) and got 17 ln(x) + 33 and 16 ln(x) + 30. It combined them. The calculator shows the spread between those two fits next to the answer, as a reminder that the result is an estimate.

A fixed multiplier says a dog ages at a steady rate all its life. The 2020 study found the opposite: dogs’ DNA changes fast early on and then slows, so the relationship between dog age and human age is a curve. That is why the old rule is too low for young dogs and too high for old ones. Where the 7× rule came from is not clear, so this page makes no claim about its origin.

The two cross by chance at about 9½ years. Before that the rule says a 1-year-old dog is 7, when the formula says 31. After that it overshoots: 84 for a 12-year-old, against about 71.

The formula has a problem with very young dogs. Because it uses a logarithm, it falls fast as age shrinks. It reaches zero at about 7.5 weeks and goes negative before that, which would give a young puppy a negative age in human years. The study’s human comparison data also start at age 1, so any answer below about 1 human year is outside the data.

What the calculator does:

• Under 8 weeks: it gives no answer, rather than a made-up one. Eight weeks is the youngest age the paper itself gives an example for, and it is where the formula comes out at about 1 human year.
• 8 weeks to 1 year: it applies the formula and marks the result as rough. A few weeks changes the answer by years in this window. The paper quotes about 9 months for 8 weeks (0.15 years). The rounded formula gives anywhere from about 8 months to 1 year there, depending on how the weeks are rounded, which shows how sensitive it is.
• Over 16 years: it still answers, but says the study did not sample dogs that old.

For puppy care, life stage matters more than a human-year number. AAHA treats a dog as a puppy until rapid growth stops, at about 6 to 9 months depending on breed and size.

Yes, in real life. In a 2020 study of 20,970 dogs at three US clinics, larger dogs had shorter lifespans, and a 2022 UK study of 30,563 dogs notes in its discussion that toy and small breeds live longer than larger ones. A 2024 preprint of 864 dogs from the Dog Aging Project reports that larger breeds show faster epigenetic ageing; its peer-review status could not be confirmed. The 2020 formula above does not model size at all, because it comes from one breed.

There is a published size-based table. AAHA hosts a poster called “My pet’s physiological age”, adapted from the Dog Owner’s Home Veterinary Handbook (Wiley, 2007). It is a rule-of-thumb table: the poster gives no method for how its numbers were made, it is not derived from DNA data, and it carries the logo of an animal-health company, Zoetis. It is included because it is the only published size-based chart that could be verified, and it is shown next to the formula so you can see how much they differ. The calculator joins the chart’s whole-year figures with straight lines for ages in between.

The chart and the formula disagree most for giant dogs and for dogs beyond 10 years: for a 10-year-old, the chart gives 56 (small) to 78 (giant), while the formula gives about 68. Neither is a measurement of your dog’s own biological age. Treat both as rough guides, and trust the life stage and your vet’s exam more than any single number.

Human-year numbers are for curiosity. The useful question is the life stage, because that sets which checks your vet will suggest. The 2019 AAHA Canine Life Stage Guidelines use four stages before “end of life” (an older 2012 version had six). AAHA says the divisions are arbitrary and phase in and out gradually, and that it does not give fixed ages for mature adult and senior, because variation increases in the later years. Instead it defines them by how much of the dog’s expected lifespan has passed (breed and size dependent).

When does senior start? AAHA’s rule is the last 25% of the dog’s expected lifespan, so a longer-lived dog is senior later. To turn that into an age, the calculator needs an expected lifespan. If you do not enter one, it uses a typical median survival time for the size class from the 2020 US clinic study:

You will see fixed ages for “senior” elsewhere, often 7 years. No single source for them could be verified, and AAHA’s 2023 senior care guidelines say there is no specific age for senior status.

A dog is 7 years 6 months old, which is 7.5 years, and weighs 28 kg.

1. Formula: ln(7.5) = 2.015. Multiply by 16 to get 32.24, then add 31. That is 63.2, about 63 human years. The paper’s two fits give 62 to 67.
2. Old rule: 7 × 7.5 = 52.5. That is about 11 years lower than the formula.
3. Size: 28 kg falls in the large band (23 to 41 kg). The chart gives 7 years = 50 and 8 years = 55, so half way is about 53.
4. Life stage: with a typical 14.6-year lifespan for this size, senior starts at about 11.0 years. At 7.5 years the dog is a mature adult, so AAHA suggests a check-up every 6 to 12 months and basic blood and urine tests about once a year, if your vet agrees.

• The formula was built mostly on Labrador Retrievers. The authors say other breeds, with different lifespans, could give different age-translation functions. For an Indian native or mixed-breed dog it is a guide, not a measurement.
• It converts age only. It does not know your dog’s health, weight, diet, or how hard its life has been.
• A dog’s body can be older or younger than its birthday suggests. Only an exam tells you that.
• If you do not know the birth date, use your vet’s estimate from the teeth and body. It will be approximate, and so will everything calculated from it.