A one-year-old dog is, biologically speaking, about 30 human years old. Not seven. This is the conclusion of a team at the University of California in San Diego, which in 2020 compared aging in the DNA of dogs and people and published a formula to translate one age into the other: human age = 16 × ln(dog age) + 31. The Cell Press press release itself notes that the old rule of multiplying by seven is incorrect.
The formula can be a bit intimidating because of the logarithm, but you can use it in ten seconds with any mobile calculator. And it has a caveat you should know before applying it to a chihuahua or a mastiff: it was calculated using Labrador retrievers.
How to do the calculation
The “ln” is the natural logarithm, a key that all scientific calculators have (also the phone calculator if you rotate it horizontally). The steps are three:
- Enter your dog’s age in years. If it is one and a half years old, enter 1.5.
- Press ln and multiply the result by 16.
- Add 31.
An example with a 4-year-old dog: the natural logarithm of 4 is 1.386. Times 16 gives 22.2. Plus 31, about 53 human years.
For those who don’t want to pull out a calculator, here are the rounded results of the formula:
- 1 year: about 31 human years
- 2 years: about 42
- 3 years: about 49
- 4 years: about 53
- 5 years: about 57
- 6 years: about 60
- 8 years: about 64
- 10 years: about 68
- 12 years: about 71
- 14 years: about 73
- 16 years: about 75
The quick takeaway is why seven is wrong. A 2-year-old dog does not have 14 human years; it has well over 40. The formula climbs very steeply at the beginning and slows down later. Between the first and second birthday the dog “ages” about eleven human years; between 14 and 16, barely two.
With puppies you have to be careful. Below one year the formula loses accuracy, and with fewer than about seven weeks of life the logarithm gives a negative human age, which doesn’t make sense. The best is to stick with the example given by the authors: an eight-week-old puppy is roughly equivalent to a human baby of nine months. In an automatic calculator, the prudent thing is to start from 1 year.
Where the formula comes from
The study was authored by Tina Wang and other researchers, with Trey Ideker (UC San Diego) as senior author, and published in the journal Cell Systems in July 2020. They collaborated with Danika Bannasch, from the University of California, Davis, and Elaine Ostrander, from the United States National Institutes of Health.
What they measured is an epigenetic clock. In plain terms: with age, DNA accumulates small chemical marks (methyl groups) at specific sites, like molecular wrinkles. That pattern changes with age in a fairly predictable way and can be compared across species. The researchers looked for marks shared by dogs and humans and how they progressed in each species.
According to the paper’s bioRxiv text, they analyzed 104 dogs aged 0.1 to 16 years, ranging from a few weeks old to very old animals. Nine were removed for insufficient coverage in DNA analysis, leaving 95 dogs. Human samples included 320 people, aged 1 to 103 years. To estimate the formula’s margin of error they repeated the calculation a thousand times with resampling.
For the late stages of life they used a simple equivalence: the 12-year average life span of a Labrador corresponds to 70 years of human life expectancy worldwide. That is why the formula yields a little over 70 years for a 12-year-old Labrador.
Development timelines line up quite well. According to the press release, an eight-week-old puppy and a nine-month-old baby are in the same phase, the phase of teething. A nine-month-old dog may already be able to have puppies, and a one-year-old dog is, in Ideker’s words, “like a 30-year-old human.”
The limit: a single breed
Here is the fine print. The formula was tuned with Labrador retrievers. The press release mentions 104 Labrador retrievers; the study text notes that the sample was “primarily” Labradors and at another point that it was focused “exclusively” on them. The authors acknowledge that breeds with very different lifespans could yield different epigenetic translation functions. Ideker adds that studying other breeds would provide more information.
In practice, that means the result is a reasonable estimate for a Labrador or a dog of a similar size, and a rougher approximation for other breeds. It should be taken as a guide, not as an exact measurement.
Why size matters
That breed matters is not a minor detail. Among dogs, something unusual happens in the animal kingdom: the big ones live shorter lives than the small ones, the opposite of what happens when you compare a mouse and an elephant.
The American Kennel Club, the major dog association in the United States, summarizes several studies in that direction. According to that summary, size is the variable that best predicts how long a dog lives, ahead of whether it is purebred or mixed. It also cites Cornelia Kraus of the University of Göttingen, who analyzed 74 breeds and more than 56,000 dogs and concluded that “big dogs age at a faster pace.” The same text notes, as an example, that German Pointers live on average around 9.63 years.
Be wary of online size-based equivalence charts. We did not find any with a study behind them, and they disagree with one another. What is documented, however, is the trend: the larger the dog, the sooner it reaches old age.
If you’re curious to compare, here you can see how long other animals live, some with numbers that would dwarf any dog’s lifespan. We also have other animal records, including the slowest, the top speeds of other animals on the far end, and how long animals sleep.
And the 15-and-9 rule
Another widely repeated count says that the first year of a dog is worth about 15 human years and the second year about 9 more. The AKC acknowledges this and does not mislead about the underlying idea—that a dog matures very quickly at first. But it says that thereafter aging depends on age and size, without giving a yearly figure, and it does not cite a study behind it. The 2020 formula, with its limitations, is for now the account with the strongest direct scientific support.
