Dog & Cat Age to Human Years Calculator
Enter your pet's age in years and months to see roughly how old it is in human years. Cats follow 15 human years at age 1, 24 at age 2, and 4 more for each year after that; dogs use the same first two years and then add 4, 5, or 6 years per year depending on small, medium, or large size. A quick-reference chart is included. Everything is calculated in your browser, and nothing you type is sent to a server. To work out a person's age or the days until a birthday, try the Age Calculator.
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Age conversion chart
| Pet age | Cat | Small dog | Medium dog | Large dog |
|---|---|---|---|---|
| 1 | 15 | 15 | 15 | 15 |
| 2 | 24 | 24 | 24 | 24 |
| 3 | 28 | 28 | 29 | 30 |
| 4 | 32 | 32 | 34 | 36 |
| 5 | 36 | 36 | 39 | 42 |
| 6 | 40 | 40 | 44 | 48 |
| 7 | 44 | 44 | 49 | 54 |
| 8 | 48 | 48 | 54 | 60 |
| 9 | 52 | 52 | 59 | 66 |
| 10 | 56 | 56 | 64 | 72 |
| 11 | 60 | 60 | 69 | 78 |
| 12 | 64 | 64 | 74 | 84 |
| 13 | 68 | 68 | 79 | 90 |
| 14 | 72 | 72 | 84 | 96 |
| 15 | 76 | 76 | 89 | 102 |
| 16 | 80 | 80 | 94 | 108 |
| 17 | 84 | 84 | 99 | 114 |
| 18 | 88 | 88 | 104 | 120 |
| 19 | 92 | 92 | 109 | 126 |
| 20 | 96 | 96 | 114 | 132 |
Notes
- The formula treats age 1 as 15 human years and age 2 as 24, then adds 4 years per year for cats and small dogs, 5 for medium dogs, and 6 for large dogs. This is a widely quoted rule of thumb from vets and pet food makers; there is no official standard, and sources differ.
- Ages under 1 and between 1 and 2 are straight-line estimates based on the number of months. In reality pets mature faster; a few months old is roughly a human teenager.
- Size groups are approximate. Breed, individual differences, lifestyle, and health all change how a pet ages. This is not a substitute for veterinary advice.
- Enter whole numbers: years 0–40 and months 0–11.
Glossary
Human-equivalent age
A rough way to express a pet's maturity and aging in human years. Pets mature within one to two years and then age faster than people, so the number is easier to picture than the calendar age.
Dog size groups
Dogs are usually grouped by adult weight into small, medium, and large. Larger dogs tend to have shorter lifespans and age faster, so more human years are added per year after age 2.
FAQ
How is a dog's or cat's age converted to human years?
Age 1 counts as 15 human years and age 2 as 24. After that, add 4 years per year for cats and small dogs, 5 for medium dogs, and 6 for large dogs. A 10-year-old cat is 24 + 4 × 8 = 56.
Why does the conversion depend on dog size?
Larger dogs tend to have shorter lifespans and age faster, so more human years are added per year after age 2. Breed and individual differences matter too, so treat the result as a rough guide.
How are puppies and kittens under 1 year handled?
The age is scaled in a straight line from 0 at birth to 15 at one year, based on months. Real pets grow very quickly in their first months, so this is only a rough estimate.
Is there an official conversion standard?
No. There is no official standard and sources give different numbers. This tool uses a commonly quoted rule of thumb and is not a substitute for veterinary advice.
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