The most common answer is that One human year equals seven dog years, so if you are now 15, then in dog years you would be 105!
However, this statement that ‘one dog year equals seven years of a human life’ is not entirely accurate. The ratio is higher with youth and decreases a bit as the dog ages. Depending on breed, a dog experiences the raging hormones of adolescence anywhere from eight months to two years or more. Generally, a dog of six years has aged about as much as a 45-year-old human. At 10, she’s like a human of 65; at 12, a human of 75; and at 15, a human of 90.
For Example: for a dog that is 11 years old
(the first two years) 10.5 * 2 = 21
(plus the next eight years) 4 * 9 = 36
21 + 36 = 57 years old
A dog’s lifespan is only a fraction of the average human’s lifespan, which means that a dog ages more quickly in the same amount of time.
In summary therefore, To calculate this, remember 10.5 dog years per human year for the first 2 years, then 4 dog years per human year for each year after.