1 dog year = 7 human years? The maths is wrong

"One dog year equals seven human years": everyone knows the rule, and it is wrong. According to a University of California San Diego study, a one-year-old dog already has the biological age of a 31-year-old adult. Here is the real formula and what it means for your dog's health.

Where does the new formula come from?

Researchers analysed blood from 104 dogs, almost all labradors, aged 4 weeks to 16 years. They measured DNA methylation, chemical marks that build up with age like invisible wrinkles. By comparing this "epigenetic clock" with the human one, they published a conversion formula in Cell Systems in 2020:

human age = 16 × ln(dog age) + 31 (ln is the natural logarithm, found on any scientific calculator).

The conversion table

Applying the formula: 1 year ≈ 31; 2 years ≈ 42; 3 years ≈ 49; 4 years ≈ 53; 5 years ≈ 57; 7 years ≈ 62; 10 years ≈ 68; 12 years ≈ 71; 14 years ≈ 73. The researchers also note that an 8-week-old puppy roughly matches a 9-month-old baby: both are teething.

The curve is very steep at first, then flattens. That is the opposite of the "×7" rule, which underestimates young dogs and overestimates old ones.

What it means for your dog's health

The first year counts double. In a few months your puppy goes through childhood and adolescence: it is the time for vaccines, socialisation and good habits.

At 7, it is in its sixties. Even if it still runs like a youngster, this is the age to discuss closer follow-up with your vet: weight, teeth, joints, blood tests as advised.

The study's limits

The formula was built on a single breed, the labrador. Small dogs generally live longer than large ones, so the exact match may vary with breed and size. It gives a far better order of magnitude than "×7", not a diagnosis.

Frequently asked questions

Does the formula work for cats?

No, it was calculated only for dogs.

How do I do the maths on my phone?

Switch the calculator to scientific mode, type the dog's age, press "ln", multiply by 16, then add 31.

Should my 8-year-old dog see the vet more often?

Discuss it with your vet, who will adapt the visit schedule to its health and breed.

Read more: the vaccine schedule in Morocco and the puppy's digital health record.

General information that does not replace a vet's advice.

Sources: Wang T. et al., "Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome", Cell Systems, 2020 (UC San Diego); NHGRI; summaries by ScienceAlert and BBC Science Focus.