Dog Age Calculator
Convert your dog's age to human years using the breed size chart, the new UC San Diego formula or the old 7-year rule, and see which life stage your dog is in
Last updated: November 9, 2026
How to Use the Dog Age Calculator
How to use the dog age calculator
- Enter your dog's age. Type the full years, and add extra months if your dog is not on an exact birthday. For a puppy, use 0 years and the number of months.
- Choose the adult size of the breed. Pick small, medium, large or giant. For a mixed breed, choose the size your dog is, or will be, as an adult.
- Pick the headline method. The breed size chart is a good default. The UC San Diego formula and the 7-year rule are always shown too, so you can compare them.
- Read the results. You see your dog's age in human years, the life stage, the age when the senior stage usually starts, and a chart for dogs from 1 to 15 years old.
These conversions are estimates. Genes, weight, diet and health all change how a particular dog ages, so use them as a guide and talk to your vet about the right care for your dog's age.
How the Dog Age Calculator Works
Why "1 dog year = 7 human years" is not right
The old rule of thumb multiplies a dog's age by 7. It is easy to remember, but it is wrong at both ends of life. A one-year-old dog is not like a 7-year-old child: most dogs are fully grown and able to have puppies by their first birthday, much like a teenager. Dogs also age at different speeds depending on their size, so a single multiplier cannot fit a Chihuahua and a Great Dane.
The breed size method
Veterinary age charts count the first two years of a dog's life as roughly 24 human years, then add a fixed number of human years for every extra dog year. The yearly amount depends on adult size:
- Small dogs (under 20 lb): 15 years for year one, 9 for year two, then 4 years for every year after
- Medium dogs (21 to 50 lb): 15 + 9, then 5 years a year
- Large dogs (51 to 90 lb): 15 + 9, then 6 years a year
- Giant dogs (over 90 lb): 12 + 10, then 7 years a year
Example: a medium dog aged 5 is 15 + 9 + (3 × 5) = 39 human years. A giant dog aged 5 is 12 + 10 + (3 × 7) = 43 human years.
The UC San Diego formula
In 2020, researchers at UC San Diego compared how DNA methylation changes with age in dogs and in people. Their result is a curve rather than a straight line:
Human age = 16 × ln(dog age) + 31
Here ln is the natural logarithm. It gives 31 human years at age 1, about 42 at age 2 and about 68 at age 10. The study used Labrador Retrievers, so it is most reliable for medium to large dogs. Below about 3 months the curve falls under zero, so this calculator draws a straight line from 0 to the curve instead.
Life stages
Most vets describe four stages: puppy (under 1 year), young adult (1 to 3 years), mature adult and senior. Small dogs reach the senior stage at around 10 years, medium dogs around 8, large dogs around 7 and giant breeds around 6.
About Dog Age Calculator
Our dog age calculator is a free, easy-to-use tool designed to help youconvert your dog's age to human years using the breed size chart, the new uc san diego formula or the old 7-year rule, and see which life stage your dog is in. For professionals or those who need quick calculations, our calculator provides accurate results instantly.
Frequently Asked Questions
How do I calculate my dog's age in human years?
The simplest accurate method uses your dog's adult size. Count the first year as about 15 human years and the second as 9 more (12 and 10 for giant breeds), then add 4, 5, 6 or 7 human years for each extra year for small, medium, large and giant dogs. The calculator does all of this for you.
Is one dog year really seven human years?
No. The 7-year rule is a rough average that does not match how dogs develop. Dogs mature much faster than 7 times in their first two years, then age more slowly, and larger breeds age faster than smaller ones.
What is the new dog age formula?
Researchers at UC San Diego found that human age is about 16 times the natural logarithm of the dog's age plus 31. It is based on DNA methylation in Labrador Retrievers, so it fits Labradors best, and other breeds may differ.
How old is a 1-year-old dog in human years?
About 15 human years by the breed size chart (12 for giant breeds), and about 31 by the UC San Diego formula. The size chart suits a young dog that has just reached physical maturity, while the formula reflects how far along the body is in biological terms.
At what age is a dog considered a senior?
It depends on size. Small dogs are usually considered seniors at around 10 years, medium dogs at 8, large dogs at 7 and giant breeds at 6. Vets often suggest a checkup every 6 months from that point.
Do small dogs live longer than large dogs?
Generally yes. Small breeds often live 12 to 16 years, while giant breeds may live only 7 to 10. Larger dogs tend to age faster, which is why the chart adds more human years per dog year for bigger dogs.
Does this work for cats or mixed breeds?
It is built for dogs. For a mixed breed, pick the size your dog is as an adult. Cats age on a different schedule, so do not use these figures for them.
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