How to use this calculator
- Enter your dog’s age in years and months. Puppies work too: put 0 years and the number of months.
- Choose your dog’s size by adult weight: small (20 lb or less), medium (21–50 lb), large (51–100 lb) or giant (over 100 lb). For a mixed breed, use its current adult weight; for a puppy, use the weight you expect it to reach.
You’ll see the human-equivalent age from the size chart, the epigenetic clock estimate, what the old ×7 rule would say, and how many human years each extra year adds at your dog’s age. The chart compares all three across a dog’s life, and the table lists every size.
Why the “×7” rule is wrong
The idea that one dog year equals seven human years is simple and popular, but it isn’t how dogs age. The American Kennel Club quotes the American Veterinary Medical Association: “Contrary to popular belief, dogs do not age at a rate of 7 human years for each year in dog years.” No one knows exactly where the rule came from; one common explanation is that it divides a roughly 70-year human lifespan by a roughly 10-year dog lifespan.
The rule gets two things wrong:
- Dogs grow up fast. Most of a dog’s development happens in its first two years, so a 1-year-old dog is more like a teenager than a 7-year-old child.
- Size matters. Large and giant breeds age faster in later life than small ones, so a single multiplier can’t fit a Chihuahua and a Great Dane.
The AVMA’s rule of thumb for a medium-sized dog is about 15 human years for the first year, about 9 more for the second, and about 5 for each year after that.
The size-adjusted chart
The chart below is the dog-years conversion chart published by the American Kennel Club, which follows that pattern and splits it by size. The last column is the epigenetic formula, computed by this calculator.
| Dog age | Small (≤20 lb) | Medium (21–50 lb) | Large (51–100 lb) | Giant (100+ lb) | Epigenetic clock |
|---|---|---|---|---|---|
| 1 | 15 | 15 | 15 | 12 | 31 |
| 2 | 24 | 24 | 24 | 22 | 42 |
| 3 | 28 | 28 | 28 | 31 | 49 |
| 4 | 32 | 32 | 32 | 38 | 53 |
| 5 | 36 | 36 | 36 | 45 | 57 |
| 6 | 40 | 42 | 45 | 49 | 60 |
| 7 | 44 | 47 | 50 | 56 | 62 |
| 8 | 48 | 51 | 55 | 64 | 64 |
| 9 | 52 | 56 | 61 | 71 | 66 |
| 10 | 56 | 60 | 66 | 79 | 68 |
| 11 | 60 | 65 | 72 | 86 | 69 |
| 12 | 64 | 69 | 77 | 93 | 71 |
| 13 | 68 | 74 | 82 | 100 | 72 |
| 14 | 72 | 78 | 88 | 107 | 73 |
| 15 | 76 | 83 | 93 | 114 | 74 |
| 16 | 80 | 87 | 99 | 121 | 75 |
For ages between whole years, the calculator interpolates in a straight line, so a 5½-year-old medium dog is 39. The chart starts at age 1; for younger puppies it scales up from birth in a straight line, which is only a rough guide during the fastest stage of growth. Past 16, it continues at the chart’s last yearly step.
The epigenetic formula (Wang et al., 2020)
In 2020, a team led by Tina Wang and Trey Ideker at the University of California San Diego published a different approach in Cell Systems. As we age, chemical tags called methyl groups build up on DNA in predictable places, a pattern known as an “epigenetic clock.” The researchers measured these patterns in 104 dogs, mainly Labrador retrievers, ranging from a few weeks to 16 years old, and matched them with the same patterns in people. The best fit was a logarithm:
Because of the logarithm, the clock runs very fast at first and slows sharply later. The paper notes that it lines up major life stages: about 8 weeks in a dog matches about 9 months in a human baby, and the typical 12-year lifespan of a Labrador corresponds to about 70 human years. The calculator gives 70.8 for a 12-year-old.
The big caveat: the formula was derived from Labrador retrievers, a large breed. The authors point out that breeds with different lifespans may need a different conversion, so for a small dog or a giant breed, lean on the size chart. The calculator also skips the formula for puppies under about 8 weeks, where it would give an age near or below zero.
Worked examples
A 5-year-old medium dog. The size chart says 36. The epigenetic formula gives 16 × ln(5) + 31 = 16 × 1.6094 + 31 ≈ 57. The ×7 rule says 35. The chart and the formula disagree most in early adulthood: the DNA clock says a 5-year-old Lab is well into middle age, while the veterinary chart says it’s in its mid-thirties.
A 10-year-old large dog. The chart says 66 and the formula says 68, very close. Here the ×7 rule gives 70, which happens to land nearby, but only by coincidence.
A 6-month-old puppy. For a small dog the chart gives about 8 (half of 15, scaled from birth), while the formula says about 20. Either way, it’s growing up fast.
Assumptions and limitations
- Every dog is an individual. Genetics, breed, weight, diet, exercise and veterinary care all affect how a dog ages. These numbers describe a typical dog, not yours specifically.
- Size categories are approximate. A 50-pound dog near the medium/large border could reasonably use either column.
- “Human years” is an analogy. It’s a way to picture your dog’s life stage, not a medical measurement.
To count your dog’s exact age from its birthday or adoption date in years, months and days, use the age calculator or the date calculator.
This calculator is for general interest and isn’t veterinary advice. Your veterinarian is the best guide to your dog’s health at every age.
Sources
- How to Calculate Dog Years to Human Years, American Kennel Club (size-based chart and AVMA guidance)
- Wang T, Ma J, Hogan AN, et al. Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome. Cell Systems 2020;11(2):176–185.e6. doi:10.1016/j.cels.2020.06.006
Frequently asked questions
Is one dog year really seven human years?
No. The American Veterinary Medical Association, quoted by the American Kennel Club, says dogs don't age at a rate of seven human years per dog year. Dogs mature far faster in their first two years, then age more slowly, and large breeds age faster than small ones. A 1-year-old dog is closer to a 15-year-old teenager than to a 7-year-old child.
How old is a 1-year-old dog in human years?
About 15 human years for small, medium and large dogs on the size chart, and about 12 for giant breeds, which mature more slowly at first. The 2020 epigenetic formula puts a 1-year-old Labrador at 31, reflecting how quickly dogs reach adulthood.
Why do big dogs age faster than small dogs?
Large and giant breeds generally have shorter lifespans than small breeds, so each year takes up a bigger share of their lives. On the size chart, a 10-year-old small dog is about 56 in human years, while a 10-year-old giant breed is about 79. Researchers are still studying why size and lifespan are linked this way in dogs.
What is the epigenetic dog age formula?
It's human age = 16 × ln(dog age) + 31, from a 2020 study by Wang and colleagues in Cell Systems. They compared age-related chemical changes to DNA (methylation) in Labrador retrievers and in people. Because it's based on one breed, it's best seen as an estimate for medium-to-large dogs.
Which method is more accurate, the chart or the formula?
Neither is exact, and they answer slightly different questions. The size chart is a veterinary rule of thumb that accounts for size; the formula is a fit to DNA data from one breed. Where they agree, you can be fairly confident; where they differ, the truth is likely somewhere in between.
When is a dog considered a senior?
It depends on size and breed, because larger dogs have shorter lives. Ask your veterinarian when to start senior wellness checks for your dog, as they'll consider its breed, size and health rather than age alone.
Updated November 2026. Results are estimates for educational purposes and depend on the inputs you provide.