This is a self-contained, premium, single-file web application. It uses a clean, modern aesthetic, high-quality typography, and real-time calculation logic. Save the following code as an `.html` file (e.g., `cat-age-calc.html`) to run it. ```html Free Cat Age to Human Age Equivalent Calculator

Cat Age Calculator

Estimate your feline's age in human years.

Select Age (Years)

0 20

Years

Human Equivalent Age

Years Old

Kitten

Developmental years. Focus on high-protein nutrition, vaccinations, and socialization to ensure a healthy start to adulthood.