Two ways to count dog years
There is no single official conversion. The calculator shows the two methods with the best footing and lets you compare them. Both agree on the big picture: dogs race through their first two years and then age more slowly, and larger dogs age faster in later life.
1. The size chart
The chart sorts dogs into four weight classes and gives a human age for each year. It was adapted from the Dog Owner's Home Veterinary Handbook (Eldredge et al., 4th ed., 2007) and is reproduced in the pet age chart hosted by AAHA. Every dog is 15 at one year and 24 at two. After that, a small dog adds about 4 human years per year and a giant dog about 7 to 8. Between whole years the calculator moves in a straight line from one row to the next.
2. The DNA-methylation formula
In 2020 researchers compared chemical marks on DNA that build up with age in dogs and in people (Wang et al., Cell Systems 11(2)). They fitted this curve:
Human age = 16 × ln(dog age in years) + 31
ln is the natural logarithm (the "ln" key on a phone calculator)
The study used 104 dogs, mostly Labrador retrievers, so it does not account for size. It suits medium to large dogs best.
Worked example: a 7-year-old, 60 lb dog
60 lb puts the dog in the 51–90 lb class, where the chart gives 50 at 7 years. The formula gives 16 × ln 7 + 31 = 16 × 1.946 + 31 = 62.1. The old ×7 rule gives 49. So this dog is roughly a person in their 50s to early 60s, and in AAHA terms a mature adult until about 9 if it is expected to live 12 years.
The size chart at a glance
| Dog age | 20 lb or less | 21–50 lb | 51–90 lb | Over 90 lb |
|---|---|---|---|---|
| 1 | 15 | 15 | 15 | 15 |
| 2 | 24 | 24 | 24 | 24 |
| 4 | 32 | 33 | 35 | 37 |
| 6 | 40 | 42 | 45 | 49 |
| 8 | 48 | 51 | 55 | 64 |
| 10 | 56 | 60 | 66 | 78 |
| 12 | 64 | 69 | 77 | 93 |
| 14 | 72 | 78 | 88 | 108 |
| 16 | 80 | 87 | 99 | 123 |
Life stages
Vets care more about life stage than about a human-age number, because stage drives checkups and screening. The 2019 AAHA Canine Life Stage Guidelines deliberately give no human-year conversion and instead define four stages:
- Puppy: birth until rapid growth stops, around 6 to 9 months depending on size.
- Young adult: until physical and social maturity, by 3 to 4 years in most dogs.
- Mature adult: from about 3 to 4 years until the last 25% of expected lifespan.
- Senior: the last 25% of expected lifespan. An end-of-life stage can come at any age.
The calculator switches from puppy at 9 months and from young adult at 3½ years. Those are midpoints, not hard lines.
Sources checked October 2026.
Questions people ask
Is one dog year really seven human years?
No. The ×7 rule makes a 1-year-old dog a 7-year-old child, but most 1-year-old dogs are sexually mature and nearly full grown, closer to a human teenager. Both the size chart and the 2020 DNA study put a 1-year-old dog at about 15 to 31 human years, and both show dogs aging fastest early in life.
Why do big dogs age faster?
Large and giant breeds have shorter lifespans, so each year counts for more of their life. On the size chart, a 10-year-old dog is 56 human years if it weighs 20 lb or less, but 78 if it weighs over 90 lb. The two sizes are the same until age 2 and split after that.
Which method should I trust?
Neither is exact. The size chart is a long-standing rule of thumb that accounts for weight. The epigenetic formula comes from measured DNA changes, but it was built mostly from Labrador retrievers, so it is best for medium to large dogs and may not fit toy or giant breeds. If the two disagree a lot, the truth is probably in between.
When is my dog a senior?
The 2019 AAHA Canine Life Stage Guidelines define senior as the last 25% of a dog’s expected lifespan. For a dog expected to live 12 years that starts at 9; for a giant breed expected to live 8 years it starts at 6. Your vet can tell you what is typical for your dog’s breed and size.
Does the calculator work for puppies?
Partly. The size chart starts at 1 year, so under 1 year you get the DNA-study estimate and the life stage only. The formula is rough for very young puppies; for example, it puts an 8-week-old puppy at about 1 human year.