Traditionally the method of calculating how old a dog is in terms of human age was to take the actual calendar years and multiply it by seven. However, research has shown that the idea of a human year being equivalent to seven dog years is inaccurate. There is no one formula for dog to human age conversion that is scientifically agreed on, although within fairly close limits they show great similarities.
Currently there are three different ways to calculate how old a dog is in terms of human maturity:
- “Popular myth” – popular myth suggests that “7 dog years equals 1 human year” or the like. This is inaccurate in two different ways, since the first year or two years represent some 18–25 years, and the ratio of human years to dog years varies with size and breed.
- “One size fits all” – suggests that the first two years equal 10.5 years each, with subsequent years equaling four human years. This is more accurate but still fails to allow for size/breed, which is a significant factor.
- Size/breed specific calculators – which try to factor in the size or breed as well. These are the most accurate types. They typically either work by expected adult weight, or by categorizing the dog as “small, medium, large”.
In general, the human equivalent of a one-year-old dog is between about 10 and 15 years—a one-year-old dog has generally reached its full growth and is sexually mature, although it might still be lanky and need to fill in a more mature musculature, similar to human teenagers. The second year is equivalent to about another 3 to 8 years in terms of physical and mental maturity, and each year thereafter is equivalent to only about 4 or 5 human years.
As in other areas, development of giant breeds is slightly delayed compared to other breeds, and, as with humans, there is a difference between adulthood and full maturity (compare humans age 20 and age 40 for example).
In all but large breeds, social interest arises around 6–9 months, emotional adulthood at around 15–18 months, and full maturity around 3–4 years, although as with humans learning and refinement continues thereafter. After that, small-breed dogs (such as a toy poodle) then become geriatric at about 11 years; medium-breed dogs (a large spaniel) at 10 years; large-breed dogs (such as Labradors) at 8 years; and giant-breed dogs (such as Mastiffs) at 7 years.
Accidents aside, life expectancy usually varies within a range. For example, a Beagle (average life expectancy 13.3 years) usually lives to around 12–15 years, and a Scottish Terrier (average life expectancy 12 years) usually lives to around 10–16 years. A random-bred dog (also known as a mongrel) has an average life expectancy of 13.2 years in the USA and much of Europe.
Anyway you look at it, it’s more important that you approximate your dogs age by other factors, like mobility, health and mental acuity. Focusing on this means you’re paying more attention to making your dog’s life happy and healthy.