Pet Age Calculator: Dog and Cat Age in Human Years

Updated November 2026 · free, works in your browser

To convert a pet's age into human years, enter its age and species in the calculator above. A 5-year-old medium dog is roughly the equivalent of a 39-year-old person, and a 10-year-old cat is roughly 56. The result is an estimate that helps you think about life stage and check-up timing, not an exact measurement.

How to use the pet age calculator

1. Choose Dog or Cat.
2. Enter your pet's age in whole years, and add extra months if needed (for example, 2 years and 6 months).
3. For a dog, pick its size group: small, medium or large, based on adult weight.
4. Read the human-year equivalent, the life stage and how many human years each additional pet year adds.

How it is calculated

The calculator uses the widely published veterinary rule of thumb that pets age much faster in their first two years and more slowly afterwards.

• The first year of life counts as 15 human years.
• The second year adds 9 more, so a 2-year-old pet is about 24 in human terms.
• Each year after that adds a fixed amount: 4 for cats and small dogs, 5 for medium dogs and 6 for large dogs.

The formula for pets older than two is: human age = 24 + (pet age − 2) × yearly rate. Months are counted as fractions of a year. Larger dogs tend to have shorter lifespans, which is why their yearly rate is higher. Newer research based on DNA changes suggests the true relationship is not a straight line, so treat every figure as an approximation.

Life stages at a glance

These stages are a general guide. Individual pets vary with breed, health and lifestyle, and your veterinarian is the best person to judge how your own pet is ageing.

Frequently asked questions

Is one dog year really seven human years?

No. The "multiply by seven" rule is a simple shortcut. Dogs mature quickly in the first two years and then age more slowly, and the rate depends on size, so a fixed multiplier is not accurate.

Why does dog size matter?

Larger dogs generally have shorter lifespans than small ones, so they reach their senior years earlier. That is why the calculator adds more human years per year for large dogs.

How do I work out my cat's age in human years?

Choose Cat and enter its age. The first year counts as 15, the second adds 9, and each year after that adds 4. A 6-year-old cat comes out at 40 human years.

What if I do not know my pet's exact age?

Use your best estimate, for example from the adoption papers, and let your veterinarian refine it. Dental wear, coat and eye clarity give clues, but they are only a rough indicator.

When should an older pet have check-ups?

Many vets suggest more frequent visits once a pet reaches its senior stage. Ask your own vet how often they recommend for your pet.

Planning ahead for an older pet

Knowing your pet's life stage helps with more than health checks. Senior pets often need shorter travel days, regular rest stops, a calm and familiar sleeping spot and easy access to water. If you plan a trip with an older companion, look for accommodation that allows pets, has ground-floor rooms or lifts, and is close to a veterinary clinic. Checking these details before you book makes the journey easier for both of you.