Dog Years Calculator: Convert Dog Age to Human Years

The “old rule of thumb” for dog years, i.e., “One Dog Year = Seven Human Years,” is simple to understand but incorrect for most dogs. A one-year-old dog is closer to a human teenager than to a seven-year-old child, and a small dog ages very differently from a giant breed later in life.

Therefore, our dog years calculator will give you two estimates: (a) a size-adjusted estimate using the chart vets commonly use; (b) the new, DNA-based formula developed as part of research conducted in 2019. Additionally, we will provide information regarding the current life-stage of your dog, with some explanation of how this affects its care.

Why the 7-Year Rule Doesn’t Work

Where did the “Seven-Year Rule” originate? No one really knows. The general consensus among researchers is that someone took an average human lifespan and divided it by an average dog lifespan and referred to the result as fact. Dogs do not grow/age at a linear pace.

Dogs age quickly during the first few months. Most dogs are able to reproduce and reach almost full maturity by the time they turn one year old. As such, a one year old dog is more like a 15-year-old human than a seven year old child. Dogs begin to slow their aging process significantly within two years of birth. From then until the end of the dog’s life, its aging will depend greatly upon size.

How Dog Years Are Actually Calculated

The size-based chart

Vets commonly refer to a chart when referring to how many human years a dog’s life is equal to. The first year of a dog’s life is equivalent to approximately 15 human years. The second year of a dog’s life is equivalent to approximately nine human years. Therefore, a 2 year old dog would be approximately 24 years old if it were human. For every additional year, small sized dogs are typically equivalent to an additional four human years while giant sized dogs are typically equivalent to an additional 7 human years.

This is the main number our calculator shows.

The DNA (epigenetic) formula

In 2019, researchers at UC San Diego compared changes in DNA methylation, a kind of chemical ageing clock, in Labrador Retrievers and humans. They came up with this formula:

Human age = 16 x ln(dog age) + 31

“ln” is called the natural log, and this will automatically compute on your calculator. The formula fits the beginning rapid aging very well. It uses only 1 breed, therefore, it does not account for size; that’s why we display the model as an additional option as opposed to a primary answer.

Dog Years to Human Years Chart

Why Small Dogs Live Longer Than Big Dogs

This is just one of those unusual things about dogs. Most mammals follow the trend where larger animals live longer (elephants live longer than mice). Within dogs, the opposite happens. For example, a Chihuahua can easily get older than 15 years of age, whereas many Great Danes do not survive beyond their first 10 years of life.

The most popular hypothesis is that due to how rapidly large breeds develop during puppyhood, there are consequences from this development. Rapid growth could potentially lead to a greater amount of cellular deterioration in the long term and possibly increase cancer risks. Regardless of what causes this trend, it indicates that at 7 years old, a Great Dane would be considered a senior pet and at 7 years old a Shih Tzu would still have approximately half its lifespan remaining.

Dog Life Stages

Generally speaking, Doodles age according to their size. For example, a Mini Goldendoodle will age more like a small dog, while a Standard Bernedoodle will age more like a large or giant breed.

Signs Your Dog Is Getting Older

• Grey hair around the muzzle and eyes
• Sleeping more and slower to get up
• Stiffness after rest, especially in the mornings
• Cloudy-looking eyes (often lenticular sclerosis, which is normal ageing, but get it checked)
• Hearing loss or not responding to their name
• Weight gain or, in older dogs, weight loss
• Changes in toilet habits or drinking more water

Increased thirst, rapid unexplained weight loss, or confusion at night are NOT simply old-age symptoms. If you notice any of these symptoms, it is time for a veterinary examination.

How to Help Your Dog Live Longer

The single most important factor in prolonging life in our pets is maintaining them as lean as possible. There was an interesting Labrador study that demonstrated that dogs that were maintained at a healthy body mass index averaged about two years more longevity than those who were obese. Following that: routine dental care; vaccinations/parasite control; appropriate daily physical activity based on their age and overall health status; and twice yearly visits with your veterinarian after the pet reaches adulthood.

Frequently Asked Questions

Vet note: Written and reviewed by Dr. Muhammad Usman, DVM. Human-year figures are estimates for fun and general guidance. Your vet will judge your dog’s age by their health, not a chart.

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