How to Add Two Decimal Numbers in Javascript

In this tutorial, you will learn how to add two decimal numbers in javascript. Addition of decimal numbers is one of the basic arithmetic operations which every newbie developer should be able to perform without any issue.  But it can also be tricky if you are trying to add 2 decimal numbers that are coming from 2 different input fields.

Almost in every programming language, we have an addition operator (+) to add one number to another and it is also present in javascript. But since the value present in the input field is of string type, we have to convert it into number type using Number() method and then do the calculation using addition operator (+).

In the following example, we have 2 input fields in which we will enter 2 random numbers. Upon click of a button, we will perform addition and display the result on the screen.  Please have a look over the code example and the steps given below.


  • We have 4 elements in the HTML file (div, input, button, and h1). The div element is just a wrapper for the rest of the elements.
  • The innerText for the button element is “Add” and for the h1 element, it is “Result”.
  • We have done some basic styling using CSS and added the link to our style.css stylesheet inside the head element.
  • We have also included our javascript file script.js with a script tag at the bottom.
<!DOCTYPE html>
<html lang="en">
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <link rel="stylesheet" href="style.css">
  <div class="container">
    <input type="number" id="firstInput" placeholder="Enter Number">    
    <input type="number" id="secondInput" placeholder="Enter Number">    

  <script src="script.js"></script>
.container {        
    text-align: center;

button {
  margin-top: 10px;
  padding: 10px 20px;

input {
  display: block;  
  margin: 10px auto;
  padding: 10px 20px;

input[type=number]::-webkit-outer-spin-button { 
  -webkit-appearance: none; 
  margin: 0; 


  • We have selected both the input elements, button element, and h1 element using the document.querySelector() method and stored them in firstInput, secondInput, btnAdd, and output variables respectively.
  • We have attached a click event listener to the button element.
  • In the event handler function, we are passing values of both the input elements to the Number() method and performing the calculation using the addition operator (+). The result is stored in the result variable.
  • We only want the result to be up to 2 decimal places and that is why we are using the toFixed() method and passing 2 as a parameter.
  • We are displaying the result in the h1 element using the innerText property.
let firstInput = document.querySelector('#firstInput');
let secondInput = document.querySelector('#secondInput');
let btnAdd = document.querySelector('button');
let output = document.querySelector('h1');

btnAdd.addEventListener('click', () =>{
    let result = Number(firstInput.value) + Number(secondInput.value);    
    result = result.toFixed(2);
    output.innerText = result;