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How do dogs age in human years?

Published: May 2021 | Updated: March 2023

If you have a dog, you have likely already heard the concept that 1 year for Rover equals 7 years for you. It turns out that the math isn't as straightforward as it seems. 

Dogs evolve faster than humans do in their early years. As a result, your furry friend's first year is roughly equivalent to 15 human years.

Size and breed are also factors. Smaller dogs live longer than larger dogs, but they may grow faster in their first few years of life. A large puppy will age more slowly at first, but by the age of five, it will be approaching middle age. Tiny and toy breeds aren't considered "seniors" until they reach the age of ten. On all counts, medium-sized dogs fall right in the middle.

Small Dog Breeds vs. Large Breeds

Scientists don't know why smaller dogs mature more slowly and live longer than larger dogs. Some experts believe it's because bigger dogs tend to be more susceptible to age-related illnesses. Bigger dogs mature faster from puppy to adult, increasing the risk of irregular cell development, cancer, and other ailments. As a result, the equation of "one dog year equals seven human years" isn't fully correct.

While the newer approach to "dog aging" is more reliable, it's still difficult to come up with a general formula for how dogs age because it depends not just on their size, but also on their breed and genetics.

Common Signs of Aging in Dogs

Observing physical and behavioral signs to assess your dog's age may be beneficial. Teeth, for example, can be an excellent predictor of your dog's age. All of your dog's permanent teeth should be in by seven months; by 1-2 years, they'll be duller and probably yellowing; and by 5-10 years, they'll be worn and potentially show some signs of disease.

If you're uncertain, you can always ask your veterinarian for a reliable estimate of your dog's age. To offer the best estimation of their age, your veterinarian will weigh factors such as teeth, body form, hair or fur, and eyes, among others. Several signs of aging include:

  • Gray hair
  • Difficulty hearing
  • Arthritis (stiffness of the joints): Stairs, jumping into the car, or even getting up after a nap can be difficult for an older dog. Her back legs can show signs of weakness. Although we all slow down as we get older, your dog's mobility problems may be the result of arthritis or another degenerative condition. You'll need to change your dog's exercise schedule to include longer, shorter walks or a new exercise routine in addition to any medicine or supplements your vet recommends. Swimming, for example, is easy on the body and popular--most dogs love it!
  • Lessened muscle tone: If or when your senior dog loses weight, you should keep a close eye on her to ensure she doesn't lose too much. This could be due to decreased muscle mass, which is normal in older dogs, or it could be due to a decrease in appetite, low nutrient absorption, or a digestive disorder. Consult your veterinarian if your dog loses more than 10% of her body mass in a few months, or even within a year.
  • Poor eyesight and/or cataracts: It's possible that you won't find eye cloudiness (nuclear sclerosis) immediately as it doesn't come on 'all of a sudden.' Instead, it's a slow, gradual process that often goes unnoticed until the eye has completely changed. Although it's a fairly normal phenomenon in senior dogs and has little effect on vision, it may also be a symptom of cataracts or other eye conditions, the majority of which are treatable. Your dog may begin to run into items or have difficulty finding a toy or other familiar objects on the floor. This could also be a sign or symptom of vision loss.
  • Difficulty holding the bladder/ incontinence: If your dog unexpectedly forgets his housetraining or strains to urinate, it may be a symptom of a urinary tract infection or kidney disease. Incontinence is common in senior dogs, and there are medications and/or supplements available to support your dog's bladder control.
  • “Dog dementia”: Canine cognitive dysfunction syndrome (CCDS) can also cause changes in behavior. CCDS, a dementia that is close to Alzheimer's in humans, can cause significant changes in your dog's normal behavior. She may feel confused, get lost, or become anxious with events that were once an everyday occurrence.
  • Bad breath: Although bad breath in dogs is normal at any age, if your dog's breath suddenly becomes unpleasant, it may be a sign of gum disease, tooth decay, or infection. As dogs age, their immune systems weaken, and they are less able to combat diseases as well as they were when they were younger. In addition to a thorough dental cleaning, your veterinarian can order blood tests to rule out infection.

If you have a larger dog, you should begin watching for signs of aging at the age of five or six, while smaller dogs might not show any signs until they are seven or eight years old. 

In any case, as your dog gets older, you'll want to pay special attention to their temperament, activity level, and eating habits. A balanced diet and healthy weight, daily mental stimulation and physical activity, and routine vet visits all contribute to extending your dog's life expectancy.

The Dog Aging Project

The Dog Aging Project aims to learn more about how genes, lifestyle, and climate affect aging in dogs. Scientists want to use the knowledge gained from dog lovers, veterinarians, and others to help dogs extend their healthspan, or the amount of time they can live life completely healthy. And, they dedicate significant effort to determining how age affects each breed individually.

The Dog Aging Project team will study tens of thousands of companion dogs over the course of ten years or more to determine the biological, lifestyle, and environmental factors that promote healthy longevity. They want to learn more about how to avoid, diagnose, and treat age-related diseases, allowing our dogs to live longer and healthier lives.

The Dog Aging Project revolves around dogs and their owners. You will have the ability to work as a citizen scientist with the research team if you nominate your dog. If you were to join, the Dog Aging Project will ask you to complete surveys about your dog's health and life. They will give you a package to collect saliva samples from your dog for genetic testing. They may also ask you to participate in specific activities with your dog and report on their results. They strive to make the experience as easy and enjoyable as possible for you and your dog. To be a part of the project, you can contact their team via their website.

The Bottom Line

We just want our dogs to live forever, and we're curious about how their age compares to human years. Keep in mind, there's no "general rule" or guideline of a dog age chart that can tell exactly what your dog's "human age" is. 

Factors including size, breed, and genetics all come into play when this determination is made.  Remember that annual visits to your veterinarian and high-quality nutrition will help prevent, detect, or delay the progression of age-related diseases, potentially extending the life of your dog.

Read More:

Here’s a Better Way to Convert Dog Years to Human Years, Scientists Say

The Dog Aging Project

NIH Researchers Reframe Dog-to-Human Aging Comparisons

Dog-to-Human Aging