Why Are Dog Years Different Than Human?

Dogs are known as man's best friend. They come in all shapes, sizes and weights, as well as lifespans. There is a difference between dog years, which are the actual age of the dog from birth, and human years, which are the equivalent age of a dog to its human counterparts. Many factors must be considered when comparing dog years and human years, including life expectancy, age, type of dog and its health.

  1. Life Expectancy

    • According to the Centers for Disease Control and Prevention, life expectancy for an average American in 2007 was 77.9 years. On the other hand, dogs have an average lifespan of seven to 15 years. Because humans live longer than dogs do, dog years must be adjusted to match human life expectancy. The longest life expectancy of dogs should equal the longest life expectancy of humans, so many years are added to each dog year for the comparison to be equivalent.

    Age

    • How dogs age differs from how humans do. This is why the old way of calculating a dog's age in human years by just multiplying the dog's age by seven is incorrect. Dogs age faster than seven human years to one dog year when they are younger. They also age a little less than seven human years to one dog year when they get toward the end of their lifespan. This is all based on when and how long adolescent hormones are produced in each dog. For a basic calculation, the first two years of a dog's life equal a total of 21 human years. The third and following years of a dogs life are each equal to four human years.

    Factors that Affect Lifespan

    • Many factors affect the lifespan of a dog. Genetics and body structure of different breeds result in some breeds having a longer life than others. In fact, small dog breeds live about 1.5 times longer than larger breeds because the body and internal organs of larger dogs have to work harder than those of smaller breeds. Female dogs live longer than male dogs. If a dog gets plenty of exercise and nutritional food, it will live longer than a dog with a less healthy life. Also, if a dog is fixed, its lifespan will be longer than if it is not.

    Average Cost of Owning a Dog

    • On average, dogs live about 10 years. The first year of a dog's life is the most expensive and costs about $970, as of 2011. This includes food, shots, spay or neuter surgery, toys, license fees and emergency vet visits. Each year after the first of a dog's life averages about $818. This amount includes a little less money for shots and accessories, and does not include a spay or neuter surgery but does include the same amount for other expenses. For the average 10-year lifespan, a dog will cost about $8,300.