How to find simple interest with JavaScript

How to find Simple Interest with JavaScript:

Let’s learn how to calculate and print the simple interest in JavaScript with examples. The program will take the values as inputs from the user and print the calculated Simple Interest.

How to calculate Simple Interest:

To calculate the simple interest, we need to get the pricipal amount, rate of interest, and the time period in years to calculate the interest. If P, r, and n are the values of the principal amount, rate of interest, and time-period, we can calculate the simple interest by using the below formula:

Simple Interest = (P * n * r)/100

We need these three values as inputs from the user and we can calculate the simple interest.

Method 1: By using predefined values:

In this method, we will use predefined principal amount, interest rate, and time period values. The program will calculate the result with the above formula.

const p = 1200;
const n = 5;
const r = 0.2;

const simpleInterest = (p * n * r) / 100;

console.log(`Simple Interest: ${simpleInterest}`);

Here, we are using predefined values for p, n, and r. The calculated simple interest is assigned to the simpleInterest variable. If you run this program, it will print the calculated simple interest value.

Simple Interest: 12

Method 2: By using user-input values:

The following example will take the values as inputs from the user and print the calculated simple interest. Create one file index.html and add the below code to it:

<!DOCTYPE html>
<html lang="en">
      function calculateSI() {
        let p = document.getElementById("inputP").value;
        let n = document.getElementById("inputN").value;
        let r = document.getElementById("inputR").value;

        let simpleInterest = (p * n * r) / 100;

        document.getElementById("result").innerHTML = simpleInterest;
    <h4>Enter the principal amount:</h4>
    <input id="inputP" />
    <h4>Enter the rate of interest:</h4>
    <input id="inputR" />
    <h4>Enter the time:</h4>
    <input id="inputN" />
    <br /><br />
    <button onclick="calculateSI()">Calculate Simple Interest</button>
    <p id="result"></p>


  • We have three input fields to take the principal value, rate of interest, and time.
  • There is one button, on clicking this button, it calls the calculateSI function. This function calculates the simple interest with the user-provided value.
    • Inside the function, it reads the value of the principal amount, interest rate, and the number of years and assigns these values to three different variables.
    • It calculates the simple interest value and assigns it to the simpleInterest variable.
    • This value is assigned to the p component result.

If you open this file in a browser, it will look as below: JavaScript example to calculate simple interest

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