Dog Age Calculator
Turn your dog’s age into human years. Enter the age in years and months, pick a size, and the calculator shows a size-based estimate and the epigenetic formula from a 2020 UC San Diego study. Everything runs in your browser.
Enter your dog’s age and press Calculate.
How to use this dog age calculator
- Enter your dog’s age in whole years and extra months. A 2 year 6 month old dog is 2 years and 6 months. Leave a box blank for zero.
- Choose the size group that matches your dog’s adult weight: small, medium, large or giant.
- Press Calculate or Enter. You get two estimates in human years, rounded to the nearest whole year. Reset clears the boxes.
Dog years to human years: how the size-based estimate works
Dogs mature quickly in their first two years and then age at a steady pace that depends on size. This calculator turns your dog’s age (years plus months divided by 12) into human years in three stages:
- Up to age 1: human age = 15 x dog age
- Between age 1 and 2: human age = 15 + 9 x (dog age – 1)
- After age 2: human age = 24 + rate x (dog age – 2), where the rate is 4 for small dogs, 5 for medium, 6 for large and 7 for giant dogs
The higher yearly rate for bigger dogs reflects the common observation that larger breeds tend to have shorter lives. It is a simple model, not a measurement.
Why “multiply by 7” is a myth
The old rule of thumb says one dog year equals seven human years. It is easy to remember but it does not fit how dogs develop. A one-year-old dog can already be fully grown and able to have puppies, which is nothing like a seven-year-old child. And a dog of 10 is not 70 in every case, because the rate depends on size and breed. The size-based estimate above gives 15 for a one-year-old and 64 for a ten-year-old medium dog, while the multiply-by-7 rule would say 7 and 70.
The epigenetic formula and its limits
In 2020, researchers at the University of California San Diego (Wang et al., published in Cell Systems) compared how DNA methylation changes with age in dogs and in humans. Their formula is human age = 16 x ln(dog age) + 31, where ln is the natural logarithm. The calculator uses it only for dogs aged 1 year or more, and shows “Not available under 1 year” otherwise.
The formula was built mainly on Labrador Retrievers, so it is an approximation for other breeds and for mixed-breed dogs. It also ignores size, which is why its answer can differ from the size-based estimate by several years.
Dog age chart: dog years to human years
| Dog age | Small | Medium | Large | Giant | Epigenetic |
|---|---|---|---|---|---|
| 1 year | 15 | 15 | 15 | 15 | 31 |
| 2 years | 24 | 24 | 24 | 24 | 42 |
| 5 years | 36 | 39 | 42 | 45 | 57 |
| 8 years | 48 | 54 | 60 | 66 | 64 |
| 10 years | 56 | 64 | 72 | 80 | 68 |
| 12 years | 64 | 74 | 84 | 94 | 71 |
| 15 years | 76 | 89 | 102 | 115 | 74 |
Worked example
A medium dog is 5 years and 0 months old. Using the size-based stages, human age = 24 + 5 x (5 – 2) = 39. Using the epigenetic formula, human age = 16 x ln(5) + 31 = 56.75, which rounds to 57. A 6 month old medium dog has an age of 0.5, so the size-based estimate is 15 x 0.5 = 7.5, which rounds up to 8 years, and the epigenetic formula is not available.
Assumptions & limits
- These are estimates for fun and rough comparison. They are not veterinary advice, and they cannot tell you how healthy your dog is. Ask your vet about your dog’s care.
- Different charts give answers that vary by a few years, because there is no single agreed formula.
- The size groups are based on adult weight. Breed, genetics and health change how a dog ages.
- The epigenetic formula comes from one study that focused on one breed.
Frequently asked questions
How old is my dog in human years?
Enter your dog’s age and size above. The size-based result and the epigenetic result are both estimates, so treat them as a range.
Why do the two results differ?
The size-based estimate changes with size, while the epigenetic formula was built on one breed and uses one curve for every dog. They can differ by several years, especially for large dogs.
Do large dogs really age faster?
Larger dogs tend to have shorter lives, which is why the size-based rate rises with size. Individual dogs vary widely.
Why does the epigenetic result say not available?
The formula uses the natural log of age and is meant for dogs aged 1 year or more. Under that age, use the size-based estimate.
What age is my dog a senior?
There is no single age. It depends on size and breed, so your vet is the best person to ask.
Can I enter months only?
Yes. Leave years blank and enter months from 0 to 11. The calculator then uses months divided by 12 as the age.
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Last updated: October 2026