Dog and Cat Age Calculator in Human Years
Dog age by size class and cat age in human years
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Updated 2026-10-04The starting values (a 5-year-old small dog) are an example. Replace them with your pet’s details.
Animal
Adult weight (size class)
The chart groups dogs by adult weight in pounds (9.07 kg, 22.7 kg and 40.8 kg are the cut-offs). Pick the closest class.
Input
0 to 30 years
0 to 11 months, added to the years.
About 36 in human years
Result
- Pet’s age
- 5 yr 0 mo
- In human years
- about 36
The math with your numbers
- Small, 20 lb or less, 5 yr → chart value 36
Small, 20 lb or less: age chart
| Pet | Human |
|---|---|
| 1 yr | 15 yr |
| 2 yr | 24 yr |
| 3 yr | 28 yr |
| 4 yr | 32 yr |
| 5 yr | 36 yr |
| 6 yr | 40 yr |
| 7 yr | 44 yr |
| 8 yr | 48 yr |
| 9 yr | 52 yr |
| 10 yr | 56 yr |
| 11 yr | 60 yr |
| 12 yr | 64 yr |
| 13 yr | 68 yr |
| 14 yr | 72 yr |
| 15 yr | 76 yr |
| 16 yr | 80 yr |
| 17 yr | 84 yr |
| 18 yr | 88 yr |
| 19 yr | 92 yr |
| 20 yr | 96 yr |
Human-year figures are a rough way to compare life stages. Pets of the same age can age at different speeds depending on breed and health. Ask your vet when to start senior check-ups.
Sources: dog size chart from the AAHA/Zoetis “Canine and Feline Age Chart” poster (dog data cited from Dog Owner’s Home Veterinary Handbook, 4th ed., Wiley 2007, Appendix B; retrieved 2026-10-04). Not checked against an AVMA table. Cat life stages from the 2021 AAHA/AAFP Feline Life Stage Guidelines (JAAHA 2021;57:51-72).
What it is
This calculator turns your dog’s or cat’s age into an approximate human age. Large dogs age faster than small ones, so for dogs you choose a size class by adult weight and the tool reads the matching column of a published age chart. For cats it starts from the commonly quoted rule and lets you change the numbers if your vet uses a different one. If you know the birthday but not the exact age, switch to birthday input and the age is counted up to today. A full chart for the selected size or rule is shown under the result.
How to use
- Choose dog or cat.
- For a dog, pick the size class from its adult weight.
- Enter the age in years and months, or switch to birthday input.
- For a cat, check the three rule values and change them if you want.
- Read the human age, the cat life stage, the formula with your numbers and the chart.
How it works
- Dogs: the size-based chart on the AAHA/Zoetis “Canine and Feline Age Chart” poster, whose dog data cites Dog Owner’s Home Veterinary Handbook (4th ed., Wiley, 2007). Six months is 10 for every size, 1 year is 15 and 2 years is 24; from age 3 the columns split by size.
- Ages between chart rows are linearly interpolated. That step is this calculator’s method, not part of the chart.
- Cats: age × 15 up to 1 year, 15 + (age − 1) × 9 up to 2 years, then 24 + (age − 2) × 4. Each number can be edited.
- Cat life stages follow the 2021 AAHA/AAFP guidelines: kitten under 1, young adult 1 to 6, mature adult 7 to 10 and senior over 10, judged on completed years.
- From a birthday, completed years plus the remaining months and days are turned into a decimal age.
Examples
| Pet | Age | Human age |
|---|---|---|
| Small dog | 5 years | 36 |
| Medium dog | 3 years 6 months | 30.5 |
| Large dog | 10 years | 66 |
| Giant dog | 7 years | 56 |
| Cat | 6 months | 7.5 |
| Cat | 10 years | 56 (mature adult) |
Good to know
Human-year figures are a convenient way to compare life stages, not a medical measure. Breed, neutering and health all change how fast an individual ages. Ask your vet when to start senior check-ups. To plan meals, try the dog food calculator too.
FAQ
Can I just multiply my dog’s age by 7?
Dogs grow very fast in their first two years, so a 1-year-old is about 15 and a 2-year-old about 24 in human terms. After that the yearly step depends on size. Multiplying by 7 makes young dogs too young and old small dogs too old (a 10-year-old small dog is 56 on the chart, not 70).
Which size class should I pick?
Use the adult weight. Small is 20 lb (9.07 kg) or less, medium 21 to 50 lb, large 51 to 90 lb and giant over 90 lb (40.8 kg).
How accurate is the cat rule?
Year 1 = 15, year 2 = 24 and 4 years for each year after that is the widely quoted rule of thumb, and sources differ slightly, so all three numbers are editable. The life stages (kitten, young adult, mature adult, senior) come from the 2021 AAHA/AAFP Feline Life Stage Guidelines.
Why does the giant column stop at 16?
The chart we use lists giant dogs only up to 16 years (123 human years). The other sizes go to 20.
How are in-between ages handled?
Between the chart’s 6-month value and its whole-year rows, the calculator draws a straight line. A medium dog is 28 at 3 and 33 at 4, so 3½ comes out at 30.5.
