Understanding Your Dog’s Age: The Truth Behind Human Years

What is a dog’s age in human years? Many people were taught that determining a dog’s “human age” is simply a matter of multiplying the dog’s age by seven. However, this is inaccurate. Correctly approximating a dog’s age in comparison to a human lifespan takes a little more calculation.

In fact, a dog’s first year adds up to 15 human years. Then, the second year adds nine years. So a two-year-old dog is 24 years old in human years. Aging during the first two years is true regardless of the size of the dog. However, from age three and up, each year adds from 4-7 human years depending on the size of the dog and their stage of life. The larger the breed and the older the dog, the more quickly they age.

Up to One Year Old

During the first year of its life, a dog will reach the equivalent of 15 human years. So, by the time a dog is a year old, it has reached adolescence. The size of the breed will determine how much a dog matures in its first year. Generally speaking, a small or toy-sized dog will have reached maturity at this age, while a giant breed will still be growing.

The first year of a dog’s life will see many changes as the dog transitions from babyhood to young adulthood. Younger puppies have high energy levels and go through stages where they chew a great deal due to teething. Once they are past the teething stage, they will begin approaching another milestone — puberty. Smaller breeds like Chihuahuas may be ready to breed in their first year, while Great Pyrenees may not reach sexual maturity until two or three years old.

Once a dog has reached its first birthday, it will have an adult appearance. As with human teenagers, dogs may continue to grow and fill out after reaching this stage. However, they are considerably more mature than young puppies and will behave more like adult dogs.

Two Years Old

Once a dog reaches its second year, it is a fully grown adult. A two-year-old dog’s physiological age in human years is 24 years old. The appearance, including the coat, will be the adult appearance that the dog will retain for most of its life. Larger breeds, particularly those considered giant-sized, will often not have their first heat cycles until their second year.

Although a dog this age is still very energetic, some of the hyper behavior often associated with puppies will have died down. Dogs this age used for working or hunting purposes will have the attention span and focus required for their appointed tasks. Once dogs reach adulthood, they are also more reliable family companions.

Four to Seven Years Old

The size of a breed will determine when a dog is considered middle-aged. Great Danes, because of their large size, are often considered middle-aged as early as four. However, a smaller dog like a Yorkie will not be considered middle-aged until closer to seven or eight years old.

Middle-aged dogs have a lower activity level than their younger counterparts. However, they are still able to perform most of the tasks demanded of them at this age. Many dogs from working breeds are highly functional into middle age and beyond.

A four-year-old dog under 20 pounds is around 32 years old in human years. Dogs larger than 90 pounds are around 37 years old in human years. A seven-year-old dog smaller than 20 pounds is 44 years of age. Dogs greater than 90 pounds are closer to 56 years of age in human years. Dogs from 21-90 pounds fall in between these age ranges.

Eight to Eleven Years Old

Although many will behave more like middle-aged dogs, most larger dogs are regarded as seniors by age eight. Medium-sized dogs are considered seniors at age 10, while the smallest breeds are considered seniors at around 11. When dogs reach the senior phase in their lives, they are likely to have visible gray hairs on their faces or other areas of their coats. On some dogs, these hairs will eventually turn white.

Dogs will usually have a decrease in their activity levels around this age. Although an older dog in good health will be somewhat active, the activity level of youth and middle age is unlikely. Age-related health problems are more common in senior dogs than in middle-aged dogs.

When dogs under 20 pounds reach eight years old, their physiological age in human years is 48 years old. For a dog over 90 pounds, the age in human years is 64. At 11 years old, dogs under 20 pounds are 60 years old, while dogs greater than 90 pounds are 86 human years old. The approximate human ages of dogs from 21-90 pounds fall in between these ranges.

Possible Exceptions to the Aging Process

Two types of dogs may age somewhat faster than others. One type is toy-sized dogs bred to “teacup” size, such as smaller Chihuahuas and Yorkshire Terriers. Teacup-size Chihuahuas and Yorkies may only live 7-12 years instead of the 14-15-year lifespans more typical of these breeds. However, this can vary based on individual health and the type of care they receive. Another example is giant breeds, including Great Danes and Irish Wolfhounds, which may have lifespans as short as 6-7 years.

Dogs that are exceptionally small or large are often the product of breeding from a very limited gene pool. Because a smaller group of dogs makes up their bloodlines, they have a higher chance of inheriting health conditions detrimental to their longevity. However, dogs bred from working lines or carefully bred performance dogs can sometimes live longer and may age somewhat more slowly.