Why Do Dogs Age Faster Than Humans?

Life at a faster pace

Species that grow quickly and reproduce early tend to have shorter lifespans. Dogs become sexually mature within their first year, and many females can have puppies before they turn two. Their bodies are built for rapid development, and that faster pace carries on through the rest of their lives.

Large dogs age faster

Among mammals, larger species usually live longer than smaller ones: an elephant far outlives a mouse. Within dogs it's the other way around. Small dogs generally live longer than large ones.

A 2013 study in The American Naturalist (Kraus, Pavard and Promislow) analysed the lifespans of a large number of dogs and found that large dogs don't just die younger, they appear to age faster once they reach adulthood. One possible explanation is that the very rapid growth of large breeds carries a cost later in life, but the mechanisms aren't fully understood.

What this means for your dog

Because large and giant breeds age faster, they also reach their senior years sooner. A giant dog may be considered a senior at around six, while many small dogs don't get there until around ten.

That's why the calculator distinguishes between sizes from the third year onward. The first two years are the same for every dog, in line with veterinary guidance. After that we use our own size-adjusted model to reflect that the pace varies.

Factors beyond size

• Weight: A lifetime study of Labrador Retrievers (Kealy et al., 2002) found that dogs kept lean throughout life lived nearly two years longer on average than littermates that were fed more.
• Genetics: Some breeds are more prone to conditions that can affect lifespan, such as heart disease or breathing problems in flat-faced breeds.
• Activity: Regular exercise and mental stimulation help keep a dog fit throughout life.
• Preventive care: Regular veterinary check-ups make it easier to catch changes early.