Dog & Cat Age Calculator
Find out how old your dog or cat is in human years, and which life stage they’re in. Advanced adds date of birth, weight, the DNA formula and human age back to pet years.
Handy for puppies and kittens.
How old would your dog be if it were this many human years old?
Dog age chart: pet years to human years
Vet chart figures are a common rule of thumb. Your row is highlighted.
How your pet’s age is worked out
Your numbers, step by step, with the common vet rule of thumb.
- 1
First year = 15
1st year → 15
- 2
Second year adds 9
15 + 9 = 24
- 3
Then +5 a year
3 yrs × 5 = 15
- 4
Add it up
24 + 15 = 39
Adult
Read more: the formulas, a worked example, the age chart and life stages
There’s no single “correct” conversion. Dogs and cats grow up very fast in their first two years, then age more slowly. Big dogs age faster than small dogs after that, which is why giant breeds usually have shorter lives. This calculator uses the common vet rule of thumb, and shows the 2020 DNA formula and the old × 7 rule beside it so you can compare.
The formula
Vet chart (rule of thumb):
first year = 15 human years
second year = +9 (24 at age two)
each year after = +4 small dog or cat, +5 medium, +6 large, +7 giant
human age = 24 + yearly step × (age − 2)
DNA formula (dogs, 2020): human age = 16 × ln(dog age) + 31
Old myth: human age = pet age × 7
Part years are spread evenly, so a 6-month-old puppy is 15 × 0.5 = 7.5. Reverse mode runs the same rules backwards: for a human age above 24, pet age = 2 + (human age − 24) ÷ yearly step.
Worked example
A medium dog aged 5 years: the first year counts as 15, the second adds 9 (24), and the next 3 years add 5 each, 3 × 5 = 15. So 24 + 15 = 39 human years, which makes it an adult. The DNA formula gives 16 × ln(5) + 31 = 16 × 1.609 + 31 = 56.8, and the old rule gives 5 × 7 = 35. On its 6th birthday it will be 39 + 5 = 44.
Rule-of-thumb steps and typical life expectancy
| Pet | Adult weight | Each year after 2 | Typical lifespan |
|---|---|---|---|
| Small dog | up to 9 kg (20 lb) | +4 | 12–16 years |
| Medium dog | 9–23 kg (21–50 lb) | +5 | 10–14 years |
| Large dog | 23–45 kg (51–100 lb) | +6 | 10–12 years |
| Giant dog | over 45 kg (100 lb) | +7 | 8–10 years |
| Cat | any | +4 | 12–18 years |
Lifespans are typical ranges only. Breed, weight, neutering, diet and care all make a big difference, and many pets live well past them. Mixed-breed dogs: pick the size they are, or will be, when fully grown.
Life stages
The stage comes from the human-equivalent age on the vet chart, so bigger dogs reach each stage sooner:
- Puppy under 1 year, or kitten under 6 months.
- Junior up to 24 in human years (about age 2).
- Adult up to 40 (cats: 3 to 6 years).
- Mature adult up to 56 (cats: 7 to 10).
- Senior up to 72 (cats: 11 to 14).
- Geriatric (super senior) after 72 (cats: 15 and over).
Many vets suggest check-ups twice a year once a pet reaches the senior stage.
About the DNA formula
In 2020, scientists at UC San Diego compared changes to DNA (an “epigenetic clock”) in 104 Labrador Retrievers with the same changes in people, and published the formula human age = 16 × ln(dog age) + 31. It shows how quickly puppies mature: a 1-year-old dog is like a 31-year-old, and a 2-year-old like 42. It was built from one breed, so treat it as a fun comparison, not a fixed rule. It gives odd results for very young puppies, and it isn’t used for cats.
Why “× 7” is a myth
Multiplying by seven makes a 1-year-old dog seem like a 7-year-old child, when most dogs that age are fully grown and can have puppies. It also misses how size changes the pace of ageing. It’s shown here only for comparison.
Common questions
How do I calculate my dog's age in human years?
The vet rule of thumb counts the first year as 15 human years and the second as 9 more, so 24 at age two. Each year after adds 4 for small dogs, 5 for medium, 6 for large and 7 for giant dogs. A 5-year-old medium dog is about 39.
Is one dog year equal to seven human years?
No, that's a myth. It makes a 1-year-old dog seem like a 7-year-old child, when most dogs that age are fully grown and can have puppies. It also misses how size changes the pace of ageing. It's shown here only for comparison.
How old is my cat in human years?
Cats start the same way as dogs on the vet chart: 15 human years for the first year and 24 at age two, then 4 more for each year after. So a 5-year-old cat is about 24 + 3 × 4 = 36 in human years.
What is the DNA formula for dog age?
In 2020, scientists at UC San Diego published human age = 16 × ln(dog age) + 31, based on DNA changes in 104 Labrador Retrievers. It says a 1-year-old dog is like a 31-year-old. It was built from one breed, so treat it as a fun comparison, not a fixed rule.
When is a dog considered a senior?
Here the senior stage runs from above 56 up to 72 in human years on the vet chart, so bigger dogs get there sooner. For cats, senior is 11 to 14 years old. Many vets suggest check-ups twice a year once a pet reaches the senior stage.
How long do dogs and cats live?
Typical lifespans are 12–16 years for small dogs, 10–14 for medium, 10–12 for large and 8–10 for giant dogs, and 12–18 years for cats. Breed, weight, neutering, diet and care all make a big difference, and many pets live well past these.
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Made by Zulu Calculator, part of AlphaZulu LLC. Formulas are shown in full and rule figures are checked against official sources; see how we build calculators.