Instructions
Determine your dog's age in fractional years before converting, since knowing the dog's age in years is not very accurate. You can do this easily in a spreadsheet with the following syntax: =ROUND(ROUND(A1-B1,0)/365,2). Here, cell A1 is the current date and B1 is the dog's date of birth.
Multiply the result in Step 1 by 7 to get the conventional meaning of "canine years" used in the popular press and conversation. For example, a dog that is 15.7 years in 365-day years is 110 years old after rounding to three digits.
Use the official formula of the American Veterinary Medical Association by counting the first year as 15 canine years and every year after that as five years. This formula applies for a midsized breed. For example, for a dog of 15.7 years, the AVMA formula gives 1*15 + 14.7*5 = 88.5 canine years.
Use another formula, which views the first two years as bringing the dog to adulthood, not just the first year. Count each of the first two years at 10.5 years. Count each year after that as four canine years. This is the basis of the calculator at onlineconversion.com.
Using the above example, 15.7 years becomes 2*10.5 + 13.7*4 = 75.8 years.
Use another formula, which views the first year as 15 canine years, the second year as nine canine years and each year after as four canine years. This is the formula used in Pedigree.com's age calculator and for the MaxiBeagle.com conversion table. This formula accounts for maturation still going on in the second year.
How to Calculate Canine Years
Canine years are the equivalent age of a dog if it were human. The object is to quantify an age that otherwise would make little sense. When ssomeone says, "My dog Rex is 50 years old," clearly a qualifier is needed, and this is where the phrase "in dog years" is useful. The accepted meaning of "canine years" in colloquial speech and in newspapers is to use a factor of seven. More sophisticated formulas and tables have evolved that take into account breed size and the varying rate of age between dogs and humans.