What this calculator does
Cat age in human years works out a cat's age converted to an equivalent human age using the standard veterinary chart. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaYear 1 ≈ 15 human years; Year 2 adds ≈9 more; each year after adds ≈4
The inputs explained
| Field | What to enter |
|---|---|
| Cat's age (years) | A number, measured in years. Starts at 3. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with cat's age
Every other input is held at the calculator’s starting values while cat's age varies. Select any row to load that scenario into the calculator.
How the answer changes with cat's age
| Cat's age (years) | Human-equivalent age | Cat age in months | Formula used |
|---|---|---|---|
| 1.5 | 19.5 years | 18.0 months | 1st year ≈ 15 human years, 2nd year ≈ +9, then +4 per year after: the standard veterinary conversion chart |
| 2.25 | 25.0 years | 27.0 months | 1st year ≈ 15 human years, 2nd year ≈ +9, then +4 per year after: the standard veterinary conversion chart |
| 3 | 28.0 years | 36.0 months | 1st year ≈ 15 human years, 2nd year ≈ +9, then +4 per year after: the standard veterinary conversion chart |
| 4.5 | 34.0 years | 54.0 months | 1st year ≈ 15 human years, 2nd year ≈ +9, then +4 per year after: the standard veterinary conversion chart |
| 6 | 40.0 years | 72.0 months | 1st year ≈ 15 human years, 2nd year ≈ +9, then +4 per year after: the standard veterinary conversion chart |
| 9 | 52.0 years | 108.0 months | 1st year ≈ 15 human years, 2nd year ≈ +9, then +4 per year after: the standard veterinary conversion chart |