Pet Age Calculator
Convert dog and cat age to human years.
Decimals such as 1.5 years are allowed.
Human age equivalent
- yrs
Enter an age.
What is pet age conversion?
Dogs and cats age at a different pace than humans, so their age is often converted to a "human age" to gauge their life stage. A common approximation treats year 1 as 15 and year 2 as 24 in human years, then adds +5 per year for dogs and +4 per year for cats beyond that.
How it is calculated
For age ≤ 1 year: human age = age × 15. Between 1 and 2 years, it interpolates linearly up to 24 using 15 + (age − 1) × 9. Beyond 2 years: 24 + (age − 2) × yearly rate, where the yearly rate is 5 for dogs (adjustable to 4.5/5/6 for small/medium/large) and 4 for cats.
When a birthday is entered, the age in years is derived from the day difference to today divided by 365.25, then the same formula applies.
Notes
This tool is based on a widely used approximation formula and is provided for general reference. Actual aging speed can vary by breed, genetics, and health condition, so please consult a veterinarian for an accurate health assessment.
Why multiplying by seven does not work
The familiar rule of seven misses how ageing actually runs: fast in the first years, slower afterwards, and different again by body size.
The first two years
A dog reaches a developmental stage near a human fifteen by its first year and around twenty-four by its second, after which roughly four or five human years are added annually.
Cats follow a similar pattern — about fifteen at one year, twenty-four at two, then four a year thereafter.
Multiplying by seven therefore badly understates puppyhood and overstates old age: a one-year-old dog is close to physical maturity, not a seven-year-old child.
Larger dogs age faster
Small dogs outlive large ones. Large breeds finish growing later yet enter old age sooner, so at the same age they are the older animal.
Conversion tables therefore split by weight band: at seven, a small dog sits in middle age while a large one is already senior.
Breed matters as well — lines prone to particular conditions need attention earlier at the same age.
What matters more than the table
Age conversion is a cue for care, not a diagnosis. As an animal turns senior, check-ups move closer together and joints, teeth, kidneys and heart warrant regular review.
Weight and diet shift with age too: activity falls and so does energy need, and keeping portions unchanged adds weight that loads the joints.
Behaviour change can signal ageing or illness. More sleep, avoiding stairs or slower responses deserve a consultation rather than being written off as age.
Legal basis
- Dog and cat age conversion — American Veterinary Medical Association guidance
- Senior thresholds by weight band — companion animal senior care guidance
- Senior health screening — Korean Veterinary Medical Association recommendations