A 21-year-old Brittany in human years
| AVMA size-based15 for year one, 9 for year two, then 5/year for a medium breed | 119human years |
|---|---|
| Epigenetic clock16 × ln(age) + 31 — Wang et al. 2020, calibrated on Labradors | 80human years |
| Difference between the twothey disagree — see the note below | -39years |
| Life stage | senior |
| Size class30–40 lb — larger dogs age faster | medium |
| Typical lifespanmedian for medium breeds | 13years |
| Share of life so far | 100% |
| Typical years remaininga population median, not a prediction about your dog | 0years |
- Breed
- Brittany
- Age
- 21 years
Two answers, and neither is simply wrong
119 human years by the AVMA size-based table: 15 for the first year, 9 for the second, then 5 a year for a medium breed.
80 human years by the epigenetic clock published in Cell Systems in 2020 — human age = 16 × ln(dog age) + 31, derived from DNA methylation.
They differ by 39 years here. The epigenetic clock is a measurement rather than a convention and captures early life remarkably well, but it was calibrated on Labradors and cannot see breed size. The AVMA table does account for size but is a smoothed consensus.
Bigger dogs age faster
This is backwards from mammals in general, and it is why no single conversion works. A medium breed adds about 5 human years per dog year after the second birthday; a small breed adds 4, a giant breed 6.5.
The old "multiply by seven" rule gets a one-year-old badly wrong in one direction and a fifteen-year-old badly wrong in the other.
Where this dog is
Life stage: senior. Roughly 100% through a typical lifespan for a medium breed, with a median of 13 years.
Those are population medians from veterinary data, not a forecast — individual dogs of every size routinely live well past them.
The one thing that moves the number
Weight. A landmark Purina lifetime study found dogs kept lean lived about 1.8 years longer than littermates fed 25% more. That is a larger effect than almost anything else within your control.
Notes
- Bigger dogs age faster, which is backwards from mammals in general and is the reason no single conversion table works. A medium breed adds about 5 human years per dog year after the second birthday; a small breed adds 4, a giant breed 6.5. The old "multiply by seven" rule gets a one-year-old badly wrong in one direction and a fifteen-year-old badly wrong in the other.
- The two methods differ by 39 years at this age, and neither is simply wrong. The epigenetic clock is measured from DNA methylation and captures early life very well, but it was calibrated on Labradors and cannot see breed size. The AVMA table does account for size but is a smoothed consensus rather than a measurement.
- At senior stage, twice-yearly vet visits are the standard recommendation rather than annual ones. Most of what shortens a senior dog's remaining time — dental disease, arthritis, kidney and heart changes — is manageable when found early and expensive when found late.
- Lifespan figures are population medians from veterinary data, not a forecast. Individual dogs of every size routinely live well past them.