Puppy and baby

Calculating Your Dog’s Age

How to Convert Dog Years to Human Years

You are probably familiar with the “multiply by 7” rule to determine your dog’s equivalent age in human years. While this is an easy way to come up with a number, research has shown that it is not very accurate.

The “multiply by 7” idea was likely derived from the average worldwide lifespans for dogs and humans, 10 and 70 years, respectively. The problem is that dogs age much more rapidly than humans do during the first years of life.

Research has revealed a new way to think about calculating a dog’s age in human years. Scientists from the University of California, San Diego, the National Institutes of Health, the University of Pittsburgh, School of Medicine, and the University of California, Davis, School of Veterinary Medicine investigated methylation patterns in the DNA of a group of 104 Labrador Retrievers aged 4 weeks to 16 years. They then compared the data with methylation patterns in humans.

Methylation is a biological process in which methyl (CH3) groups are added to DNA molecules. This can change DNA activity without changing the DNA sequence. As both humans and dogs get older, methyl groups are added to their DNA, enabling the use of mathematical models known as “molecular clocks” to measure age.

The data showed that major developmental milestones lined up between the two species. The first 8 weeks of a dog’s life aligned well with the first 9 months in humans, and culminated in life expectancies of 12 and 70 years, respectively. The researchers developed the following equation to calculate a dog’s age in human years based on this information: human age = 16 ln(dog age) + 31. The abbreviation “ln” stands for the natural log. The comparable life stages break down like this:

Comparison of age in dogs and humans.
Dogs' Age Humans' Age
First 8 weeks First 9 months
2 - 6 months 1 - 12 years
6 months - 2 years 12 - 25 years
2 - 7 years 25 - 50 years
7 - 12 years 70 years

This research highlighted the fact that dogs have a comparatively long twilight period, suggesting that focusing on canine geriatrics could be important and highly relevant to canine health.

It should be noted that this study looked at one breed of dog, the Labrador Retriever, and we know that breeds age differently. Small dogs tend to live longer than large dogs. Additional studies will be needed to determine how this calculation might change for different breeds.

The American Veterinary Medical Association (AVMA) and the American Kennel Club (AKC) use the following guidelines for calculating a dog’s age:

  • One year of age for a medium-sized dog is equivalent to 15 years of age for a human.
  • Two years of age for a dog equals 9 years of age for a human.
  • Subsequently, each human year is equivalent to 5 years for a dog.

The AVMA considers small dogs “senior” beginning at 7 years of age, whereas larger breeds are considered “senior” at 5 or 6 years of age.

These calculations are rough estimates, but they can help you and your veterinarian provide the best care for your dogs as they age. Dogs live with us, share our environments, and suffer from many of the same age-related conditions. Understanding your dog’s age and biological life stage is important in considering age-related health issues such as arthritis, weight control, and declines in hearing or vision.

For more information:

Wang, T., Ma, J., Hogan, A.N., Fong, S., Licon, K., Tsui, B., Kreisbuerg, J.F., Adams, P.D., Carvunis, A-R, Bannasch, D.L., Ostrander, E.A., and T. Ideker. Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome. Cell Systems 11(2): 176-185.

American Kennel Club - How to calculate dog years to human years

American Veterinary Medical Association - Senior Pets

*This article may not be reproduced without the written consent of the UC Davis School of Veterinary Medicine.

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