The UCSD epigenetic formula

Our primary calculation is based on research published by Tina Wang and colleagues at the University of California, San Diego in the journal Cell Systems in July 2020. The study, "Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome," mapped how DNA methylation patterns change as dogs age, and compared those patterns to human aging signatures.

The resulting formula:

Human age = 16 × ln(dog age) + 31

Plug in a 1-year-old dog and you get 31. A 5-year-old gives you about 57. A 10-year-old, about 68. The logarithmic shape captures what generic formulas miss: dogs age fast early, then more slowly.

Limitations: the study used 104 Labrador Retrievers. It doesn't perfectly reflect how all breeds age. But it's the best general-purpose biological formula available, and it represents a major improvement over the outdated 7:1 rule.

How we handle puppies

The UCSD formula is designed for dogs one year and older — the logarithm breaks down at very small values. For puppies, we linearly interpolate up to the formula's baseline at age 1 (31 human years), which approximates the rapid early-life aging that's been observed consistently in veterinary literature.

Breed-specific lifespan data

Alongside the epigenetic formula, we report breed-specific life stages using lifespan data drawn from:

American Kennel Club breed standards (AKC.org)
The Kennel Club (UK) breed information
O'Neill et al. (2013), "Longevity and mortality of owned dogs in England" , The Veterinary Journal
Salt et al. (2019), "Longevity and mortality in UK Labrador Retrievers", PLoS ONE
McMillan et al. (2024), "Longevity of companion dog breeds", Scientific Reports

These sources give us the median expected lifespan for each breed, which we use to calculate where your dog is in their life journey — puppy, adult, senior, or beyond.

The classic AAHA method

For comparison, we also reference the size-adjusted method popularized by the American Animal Hospital Association (AAHA):

First year of life: 15 human years
Second year: 9 more human years (so age 2 = 24 human years)
Each year after:
- Small breeds: +4 human years
- Medium breeds: +5 human years
- Large breeds: +6 human years
- Giant breeds: +7 human years

This method is simpler and doesn't require a calculator, but it's rougher than the epigenetic approach.

What we can't capture

No formula can account for your individual dog's genetics, diet, weight history, dental health, exercise patterns, or medical history. These factors can meaningfully shift biological age in either direction. A lean, active, dentally-healthy 10-year-old Labrador may be biologically closer to a 60-year-old human than a 70-year-old.

For your individual dog's real biological age, your veterinarian — armed with bloodwork, physical exam findings, and history — is the best source of truth. Our calculator is a useful starting point, not a replacement.

References

Wang, T., et al. (2020). Quantitative translation of dog-to-human aging by conserved remodeling of the DNA methylome. Cell Systems, 11(2), 176–185.
Kraus, C., et al. (2013). The size-life span trade-off decomposed: why large dogs die young. The American Naturalist, 181(4), 492–505.
O'Neill, D. G., et al. (2013). Longevity and mortality of owned dogs in England. The Veterinary Journal, 198(3), 638–643.
Salt, C., et al. (2019). Longevity and mortality in UK Labrador Retrievers. PLoS ONE, 14(5).