Compound Interest Calculator

A simple yet powerful web-based compound interest calculator that helps you understand the growth of your investments over time. This calculator takes into account both initial principal and monthly investments, providing a detailed year-by-year breakdown of your investment growth.

Features

Calculate compound interest with monthly contributions
30-year investment projection
Monthly compounding frequency
Detailed breakdown including:
- Principal amount
- Interest earned
- Total balance
User-friendly interface
Responsive design
Real-time calculations

How to Use

Enter your initial investment amount in the "Initial Principal" field
Input your planned monthly contribution
Set your expected annual interest rate (as a percentage)
Click "Calculate Returns" to see your investment growth projection

Technical Details

The calculator is built using:

HTML5
CSS3
Vanilla JavaScript
Responsive design principles

Calculations

The calculator uses the following approach:

Compounds interest monthly
Adds monthly investments after applying interest
Shows yearly summaries of:
- Total principal invested (initial + monthly contributions)
- Interest earned during the year
- Total balance at year end

Example

If you start with:

Initial Principal: $1,000
Monthly Investment: $100
Annual Interest Rate: 7%

The calculator will show you:

Year-by-year growth
Total principal invested
Interest earned each year
Running balance

Usage Notes

All monetary inputs should be in dollars ($)
Interest rate should be entered as a percentage (e.g., 7 for 7%)
Results are displayed for a 30-year period
Calculations assume monthly compounding

Implementation Details

The calculator performs real-time calculations using JavaScript and updates the display immediately. Results are formatted in a clear, tabular format for easy reading and analysis.