How dog years convert to human years
The "multiply by seven" rule is a myth. Dogs grow up very fast: a one-year-old dog is roughly as developed as a 15-year-old person, and a two-year-old is comparable to a young adult in their mid-20s. After that, aging slows, but how much it slows depends on size. Large and giant breeds age faster and have shorter lifespans than small dogs.
The default method here is the rule of thumb published by the American Veterinary Medical Association (AVMA): the first year equals about 15 human years, the second adds about 9, and each year after that adds roughly 4 to 7 human years depending on size. Size-based charts from AKC and many vet clinics follow the same pattern, with small differences in the exact numbers, so expect other calculators to be a year or two apart.
The formulas
age 1 = 15 human years, age 2 = 24 human years
over 2: human age = 24 + (dog age − 2) × Y
Y = 4 small, 5 medium, 6 large, 7 giant
Epigenetic (UCSD) formula, age 1 and up:
human age = 16 × ln(dog age) + 31
The epigenetic formula
In a study published in Cell Systems (preprint 2019, journal 2020), researchers at UC San Diego tracked age-related chemical marks on DNA, called methylation, in 104 Labrador retrievers and compared them with human data. The best fit was a logarithm: dogs race through the equivalent of human childhood and early adulthood in a couple of years, then the curve flattens. "ln" is the natural logarithm. The formula only makes sense from age 1; below that it drops toward zero and then goes negative. Because it came from a single breed, it doesn't account for size, which is why this calculator uses the size-based chart by default and shows the epigenetic answer for comparison.
Example: a 5-year-old medium dog
| Step | Result |
|---|---|
| First two years | 24 |
| Three more years × 5 (medium) | +15 |
| Human-equivalent age (chart) | 39 years |
| Epigenetic: 16 × ln(5) + 31 = 16 × 1.609 + 31 | 57 years |
| Life stage | Mature adult (senior from about 9) |
The big gap is typical for middle-aged dogs: the epigenetic curve ages dogs quickly in early life, while the chart spreads aging more evenly.
Dog age chart by size
| Dog age | Small | Medium | Large | Giant | Epigenetic |
|---|---|---|---|---|---|
| 1 | 15 | 15 | 15 | 15 | 31 |
| 2 | 24 | 24 | 24 | 24 | 42 |
| 4 | 32 | 34 | 36 | 38 | 53 |
| 6 | 40 | 44 | 48 | 52 | 60 |
| 8 | 48 | 54 | 60 | 66 | 64 |
| 10 | 56 | 64 | 72 | 80 | 68 |
| 12 | 64 | 74 | 84 | 94 | 71 |
| 14 | 72 | 84 | 96 | 108 | 73 |
| 16 | 80 | 94 | 108 | 122 | 75 |
Life stages
The 2019 AAHA Canine Life Stage Guidelines group dogs into puppy, young adult, mature adult and senior, with senior defined as the last 25% of the expected lifespan rather than a fixed birthday. This calculator uses these approximate cut-offs:
- Puppy: under 1 year (under 18 months for giant breeds, which keep growing longer).
- Young adult: until about 3 years.
- Mature adult: from 3 years until the senior stage.
- Senior: from about 10 years (small), 9 (medium), 8 (large) or 6 (giant).
Keep in mind
Human-year equivalents are a way to picture your dog's age, not a biological test. Genetics, body weight, exercise and dental health all affect how an individual dog ages; keeping a dog lean is one of the best-documented ways to add healthy years. Slowing down, stiffness, weight changes or increased thirst are worth a vet visit at any age.
This calculator is for general information and is not veterinary advice.
Frequently asked questions
How old is my dog in human years?
Using the AVMA rule of thumb, a dog's first year equals about 15 human years and the second adds about 9 more, so a 2-year-old dog is roughly 24. After that, add about 4 years per year for small dogs, 5 for medium, 6 for large and 7 for giant breeds. A 5-year-old medium dog is about 39.
Is one dog year really seven human years?
No. The one-to-seven rule is a myth. Dogs mature much faster than people in their first two years, then age more slowly, and the pace after that depends on size. Big dogs age faster than small dogs.
Why do large dogs age faster than small dogs?
Nobody knows for certain, but large and giant breeds grow extremely fast and have shorter average lifespans, often 8 to 12 years versus 13 to 16 for small breeds. That is why the chart adds more human years per year as size increases, and why big dogs are considered senior sooner.
What is the epigenetic dog age formula?
A study from UC San Diego compared DNA methylation changes in 104 Labrador retrievers with those in humans and proposed human age = 16 × ln(dog age) + 31. It ages young dogs very quickly: a 1-year-old dog comes out at 31 and a 2-year-old at about 42, then the curve flattens. It was built on one breed, so treat it as an interesting comparison rather than a precise answer.
When is a dog considered a senior?
The AAHA canine life stage guidelines define senior as the last 25% of a dog's expected lifespan. That works out to roughly 10 years for small dogs, 9 for medium, 8 for large and about 6 for giant breeds. Senior dogs benefit from checkups every 6 months.
How can a vet estimate my dog's age?
Vets look at teeth, eyes, coat, joints and muscle tone. Puppies can be aged fairly accurately by which teeth have come in, but estimates for adult dogs are rough and often span several years.
Rates and figures last checked September 2026.
This calculator gives estimates for planning. Check current rates and product labels before you buy, list or file.