I Built a Simple Interest Calculator with HTML, CSS, and Vanilla JavaScript

Source: Dev.to

Introduction

I built a simple interest calculator as a small side project to practice handling user inputs and calculation logic using vanilla JavaScript. The goal was to keep it clean, simple, and easy to use.

Features

• Calculates simple interest instantly
• Clean and minimal UI
• Responsive layout for mobile devices
• Focused tool that does one thing well and is easy to understand
• Reusable in small projects

Technologies Used

• HTML – form inputs and structure
• CSS – spacing, layout, and responsiveness
• Vanilla JavaScript – interest calculation logic, input validation, and real‑time result updates

Implementation Details

HTML

Provides the form fields for principal, rate, and time, along with a container for displaying the result.

CSS

Handles spacing, flexbox/grid layout, and media queries to ensure the calculator looks good on both desktop and mobile screens.

JavaScript

• Implements the simple interest formula
• Validates user input to prevent errors
• Updates the result instantly as the user types

Demo & Source Code

• Live demo: https://yuvronixstudio.github.io/interest-calculator/
• Source code: https://github.com/YuvronixStudio/interest-calculator/

Conclusion

Simpler tools are easier to test and improve. Clear input labels reduce user errors, and small projects are great for sharpening fundamentals. I’m continuing to build small, practical web tools, and feedback or suggestions are welcome.