How do you convert dog years to human years?
Converting dog years to human years starts with the first two years, which count for the most: about 15 human years for the first and 9 for the second. From the third birthday on, the calculator adds a fixed number of human years for every dog year, and that number depends on how big your dog is as an adult.
The shape comes from the American Veterinary Medical Association, whose guideline for a medium-sized dog is 15 years, then 9, then about 5 a year. Small dogs live longer on average and giant dogs shorter, so the yearly step after two is 4 for small dogs, 5 for medium, 6 for large and 7 for giant dogs.
Dog years to human years chart by size
The chart below uses exactly the maths the calculator uses, from 1 to 16 dog years. Sizes are based on adult weight: small up to 20 lb, medium 21–50 lb, large 51–100 lb, giant over 100 lb.
| Dog age | Small | Medium | Large | Giant |
|---|---|---|---|---|
| 1 | 15 | 15 | 15 | 15 |
| 2 | 24 | 24 | 24 | 24 |
| 3 | 28 | 29 | 30 | 31 |
| 4 | 32 | 34 | 36 | 38 |
| 5 | 36 | 39 | 42 | 45 |
| 6 | 40 | 44 | 48 | 52 |
| 7 | 44 | 49 | 54 | 59 |
| 8 | 48 | 54 | 60 | 66 |
| 9 | 52 | 59 | 66 | 73 |
| 10 | 56 | 64 | 72 | 80 |
| 11 | 60 | 69 | 78 | 87 |
| 12 | 64 | 74 | 84 | 94 |
| 13 | 68 | 79 | 90 | 101 |
| 14 | 72 | 84 | 96 | 108 |
| 15 | 76 | 89 | 102 | 115 |
| 16 | 80 | 94 | 108 | 122 |
What is the UC San Diego dog age formula?
The UC San Diego formula estimates a dog's human age from changes in its DNA: human age equals 16 times the natural logarithm of the dog's age, plus 31. Researchers fitted it on DNA methylation in 104 Labrador Retrievers (Wang et al., Cell Systems, 2020). A 1-year-old dog comes out at 31 and a 4-year-old at about 53.
The formula ages young dogs much faster than the AVMA rule and older dogs more slowly. Because it was built on one breed, the calculator shows it as a second opinion rather than the main answer, and only from the first birthday, where the logarithm stops giving nonsense.
Why isn't one dog year equal to seven human years?
The seven-year rule fails because dogs grow up far faster than people at the start and then slow down. A 1-year-old dog can usually have puppies, which a 7-year-old child cannot, and a 10-year-old Great Dane is old while a 10-year-old Chihuahua may have years ahead of it. Any single multiplier gets both ends wrong.
How old is my dog in human years if it is a mixed breed?
For a mixed-breed dog, use the size it is now as an adult, or the size you expect if it is still a puppy. A mix that will weigh 35 pounds is a medium dog for this calculator, whatever its parents were. If you are unsure, run both neighbouring sizes and treat the range as the answer.
What the calculator cannot tell you
- It cannot see your dog's health, weight history or breed-specific conditions.
- It does not replace a vet's assessment of when to switch to senior care.
- The size cut-offs are a rule of thumb; a 21-pound dog is not suddenly older than a 20-pound one.
Dog age calculator FAQ
How old is a 1-year-old dog in human years?
About 15. The American Veterinary Medical Association's rule counts a dog's first year as 15 human years for every size, because dogs reach adolescence and sexual maturity within about 12 months.
Is one dog year really seven human years?
No. The seven-year rule is a myth that ignores how fast dogs grow up. By the size-adjusted AVMA rule a 2-year-old dog is about 24 in human years, not 14, and after that small dogs age more slowly than giant dogs.
Why do big dogs age faster than small dogs?
Large and giant breeds have shorter average lifespans than small breeds, so each year after the second counts for more. This calculator adds 4 human years a year for small dogs and 7 for giant dogs.
When is a dog a senior?
Roughly from 10 years for small dogs, 8 for medium dogs, 7 for large dogs and 6 for giant dogs. Your vet may suggest twice-yearly check-ups from that point.
How accurate is a dog age calculator?
It gives a useful estimate, not a medical age. Breed, genetics and health all shift how a dog ages, and the two methods here can differ by several years. Ask your vet if you need to know how your own dog is ageing.
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