About the Dog & Cat Age Calculator
The old โone dog year equals seven human yearsโ rule is wrong. Dogs and cats grow up fast in their first two years and then age more slowly โ and bigger dogs age faster than small ones. This calculator uses the size-based dog age chart cited by the AVMA and AKC and the AAFP / International Cat Care cat age chart, then places your pet in a life stage according to the AAHA and AAFP guidelines.
For dogs it also shows the result of the 2019 epigenetic clock formula based on DNA methylation.
How to use
- Choose dog or cat. For dogs, pick the size by expected adult weight.
- Enter the age in years and months, or tap Birthday and choose the date of birth.
- The human-age equivalent, life stage and care tips appear instantly.
- Use the chart below to see what your pet's age will be in human years in the coming years.
How the conversion works
- Dogs: year 1 โ 15 and year 2 โ 24 human years for most sizes. After that, small dogs add about 4 years per year, large dogs 5โ6 and giant dogs about 7. Giant breeds mature a little later (1 year โ 12).
- Cats: 6 months โ 10, 1 year = 15, 2 years = 24, then +4 per year. Example: a 10-year-old cat = 24 + 4 ร 8 = 56.
- Epigenetic formula: human age = 16 ร ln(dog age) + 31, from a study comparing DNA methylation in Labrador retrievers and humans (Wang et al., preprint 2019, Cell Systems 2020). A 2-year-old dog gives 16 ร 0.693 + 31 โ 42.1 years, so young dogs come out much โolderโ. It was derived from a single breed, so treat it as a curiosity.
Life stages (AAHA & AAFP)
| Stage | Dogs (AAHA 2019) | Cats (AAHA/AAFP 2021) |
|---|---|---|
| Puppy / kitten | Until rapid growth stops (usually 6โ9 months, longer in large breeds) | 0โ1 year |
| Young adult | Until physical and social maturity (about 3โ4 years) | 1โ6 years |
| Mature adult | Until the last 25% of expected lifespan | 7โ10 years |
| Senior | Last 25% of expected lifespan | Over 10 years |
| End of life | Any age, when terminal illness makes comfort and quality of life the focus | |
The calculator assumes expected lifespans of 15 (small), 13 (medium), 11 (large) and 9 years (giant). Real lifespans vary by breed and health.
Sources
- AAHA, 2019 Canine Life Stage Guidelines
- AAHA/AAFP, 2021 Feline Life Stage Guidelines
- AVMA / AKC, size-based dog age chart (โHow to calculate dog years to human yearsโ)
- International Cat Care, cat years to human years chart
- Wang T. et al., โQuantitative translation of dog-to-human aging by conserved remodeling of the DNA methylomeโ, Cell Systems, 2020
FAQ
Is one dog year really seven human years?
No. Dogs reach the equivalent of a mid-teen human in their first year, so a 1-year-old dog is about 15 and a 2-year-old about 24. The ร7 rule is a myth.
Why do big dogs come out older?
Large and giant breeds have shorter lifespans and age faster. At 10 years a small dog is about 56 in human years, a giant dog about 79.
When is a cat considered senior?
The 2021 AAHA/AAFP Feline Life Stage Guidelines call cats over 10 years senior. From then on, exams every 6 months with kidney, thyroid and blood-pressure checks are recommended.
Which size should I pick for a mixed-breed dog?
Use the expected adult weight. For a puppy, estimate from the parents' size or ask your vet.