The old cliché is that every year of a dog’s life is equivalent to seven human years. In other words, a five-year-old dog is like a 35-year-old human. But it’s not so simple. The rate at which dogs develop is different than for humans, and the dog’s size and breed make a big difference to its lifespan.
Humans take 18 years to reach adulthood, but puppies are only pups for six to nine months (depending on the size and breed). Dogs typically undergo puberty between six months to a year, so that’s their teenage phase. Then they count as young adults until they get to three to four years.
The lifespan of a dog
The American Animal Hospitals Association considers the last 25 per cent of a dog’s life to be when they’re old. Typically this is assumed to be around seven years of age, although it varies based on the breed (between five and ten years, say). A human life expectancy of almost 81 in the UK would put a seven-year-old dog at about 61 human years.
If you’re wondering about those breeds like the Great Dane that have short lifespans, it’s been suggested that since research shows they’re not ‘aged’ in terms of their behaviour or neurology when they die, these dogs sadly don’t get to reach old age.
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Then there’s the differing lifespan of different breeds or mixes to take into account. A recent study of almost 2 million dogs who are clients of over 1,000 vet clinics in the US found the life expectancy of a dog when they’re born is 12.69 years.
This is a little bit higher than an earlier study in the UK, which put it at 11.23 years, and a bit lower than another US study, which found it was 15.4 years.
But it depends. Female dogs live slightly longer than male dogs. Small dogs live quite a bit longer than big dogs – small dogs for 16.2 years and giant dogs for 12 years according to one study. In general, mixed-breed dogs live a little longer than pedigrees, but some purebred dogs have long lifespans (chihuahuas, shih tzus and dachshunds were the longest-lived breeds in one study).
Dog age chart: How old is my dog?
All of this tells us that a one-year-old dog is maybe the equivalent of an 18-year-old human, and perhaps after that, the 1:7 ratio makes more sense. Another line of research takes a biological approach instead.
As we age, there are epigenetic changes to DNA as a result of a process called methylation. Scientists looked at these changes in the nucleic acid (called methylomes) of 104 labradors and compared them with those of humans. The relationship was not linear. The results give us a different calculator: to find the human equivalent of a dog’s age, take the log of that age, multiply by 16, and then add 31.
It works best at either end of the lifespan and not quite so well for some of the middle years. Based on the epigenome, these scientists say an eight-week-old puppy is equivalent to a nine-month-old baby, and a 12-year-old dog is roughly equivalent to a 70-year-old person.
They also found a one-year-old dog as being equivalent to a 31-year-old human; a two-year-old dog as just over 40; a dog at seven as equivalent to a 60-year-old person; and a 14-year-old dog at around 80 in human terms.
Of course, these results will vary for other dogs. If this is starting to sound a bit depressing because your dog is older than you thought, take heart.
One large study shows that a longer life is associated with your dog being a healthy weight, so keeping an eye on their weight will help (ask your veterinarian for advice). For example, a normal-weight labrador lives 13.6 years if female and 13.3 if male, but if overweight that drops to 13.0 and 12.7 respectively.
A normal weight yorkshire terrier lives 15.5 years (female) or 16.2 (male), but that drops to 13.5 or 13.7, respectively, if overweight.
Dental cleanings are also linked to a longer lifespan, but it’s not clear if this reflects better general health care or is specific to dental care. So calculating a dog’s age in human terms is more complicated than you might think, with the weeks and months of puppydom counting for a lot, even though they’re over in a flash.
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