How to use this dog age calculator
Enter your dog's age in years and months, then choose its adult size. For mixed breeds, use the weight your dog is now (or is expected to reach). The large number is your dog's age in human years from the size-based chart that vets commonly use. Below it you'll find your dog's life stage, the age at which dogs of that size are usually considered seniors, and a second estimate from a 2020 DNA study.
Is one dog year really seven human years?
No. The "multiply by seven" rule is easy to remember, but it doesn't match how dogs develop. Dogs grow up very fast: a one-year-old dog is physically and sexually mature, much like a 15-year-old person, and a two-year-old dog is roughly like a person of 24. After that, aging slows down. How much it slows depends on size, because large and giant breeds age faster and have shorter lives than small breeds.
The American Veterinary Medical Association summarizes the usual approach this way: the first year of a medium-sized dog is about 15 human years, the second year adds about 9, and each year after that adds about 4 to 5. This calculator uses that pattern, with a slower pace for small dogs and a faster pace for large and giant dogs.
Dog years to human years chart
| Dog's age | Small ≤ 20 lb | Medium 21–50 lb | Large 51–90 lb | Giant > 90 lb |
|---|---|---|---|---|
| 1 year | 15 | 15 | 15 | 12 |
| 2 years | 24 | 24 | 24 | 22 |
| 3 years | 28 | 28 | 28 | 31 |
| 4 years | 32 | 32 | 32 | 38 |
| 5 years | 36 | 36 | 36 | 45 |
| 6 years | 40 | 42 | 45 | 49 |
| 7 years | 44 | 47 | 50 | 56 |
| 8 years | 48 | 51 | 55 | 64 |
| 9 years | 52 | 56 | 61 | 71 |
| 10 years | 56 | 60 | 66 | 79 |
| 11 years | 60 | 65 | 72 | 86 |
| 12 years | 64 | 69 | 77 | 93 |
| 13 years | 68 | 74 | 82 | 100 |
| 14 years | 72 | 78 | 88 | 107 |
| 15 years | 76 | 83 | 93 | 114 |
| 16 years | 80 | 87 | 99 | 121 |
Worked example: a 5-year-old Border Collie (medium) is about 36 in human years. A 10-year-old Labrador (large) is about 66, and a 10-year-old Great Dane (giant) is about 79. For ages between whole years, the calculator works out a value between the two chart rows.
The DNA-based formula
In 2020, researchers at the University of California San Diego compared chemical changes in the DNA of Labrador retrievers and people as both age. They published this formula in the journal Cell Systems:
Human age = 16 × ln(dog's age in years) + 31
Here "ln" is the natural logarithm. The formula says dogs age extremely fast early in life: by this measure, a 2-year-old dog is already about 42, and a 5-year-old is about 57. It was built from one breed, so it's best treated as an interesting second opinion rather than a replacement for the size-based chart.
Dog life stages
The American Animal Hospital Association (AAHA) divides a dog's life into stages rather than strict ages:
- Puppy: from birth until growth slows, at about 6 to 12 months (up to 18 months or more for giant breeds).
- Young adult: from the end of puppyhood until about 3 or 4 years.
- Mature adult: from then until the last quarter of the dog's expected lifespan.
- Senior: the last quarter of expected lifespan. That is around 10 years for many small dogs, but as early as 6 or 7 for giant breeds.
Most vets recommend a checkup once a year for adult dogs and every six months for seniors, because problems such as kidney disease, arthritis and dental disease are easier to manage when they're found early.
Why do small dogs live longer?
Across most animals, bigger species live longer. Dogs are an exception: a Chihuahua often lives into its mid-teens, while a Great Dane is considered old at 7 or 8. Researchers think large breeds grow so fast that age-related damage, including cancer, builds up sooner. Breed matters too: some small breeds with flat faces have shorter lives than their size would suggest.
Frequently asked questions
How old is a 1-year-old dog in human years?
About 15 human years for most dogs. A one-year-old dog has finished most of its growing and is sexually mature, much like a teenager. Giant breeds mature more slowly and are closer to 12.
How old is a 10-year-old dog in human years?
About 56 for a small dog, 60 for a medium dog, 66 for a large dog and 79 for a giant breed. Large and giant dogs are usually seniors well before age 10.
At what age is a dog considered a senior?
It depends on size. Small dogs are usually seniors from about 10, medium dogs from about 9, large dogs from about 8, and giant breeds from about 6 or 7.
How do I calculate my dog's age in human years?
Count the first year as about 15 human years and the second year as about 9 more, for 24 at age two. After that, add about 4 years per year for small dogs, 5 for medium dogs, 5 to 6 for large dogs and 7 or more for giant breeds. This calculator does it for you.
How can I tell how old a rescue dog is?
A vet can estimate age from the teeth (puppies get adult teeth at about 4 to 7 months, and tartar and wear build up over the years), the eyes, coat graying, and muscle and joint condition. The estimate is usually reliable within a few years for adult dogs.
Human-year values are estimates for comparison only. Individual dogs age differently depending on breed, genetics, weight and health.