How to Build an Age Calculator App using HTML, CSS, and JavaScript

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Are you interested in learning how to create an age calculator app using HTML, CSS, and JavaScript? In this tutorial, we will walk you through the step-by-step process of building an age calculator app. This small JavaScript project can be a great addition to your portfolio. So let’s get started!

Creating the HTML Structure and CSS Style

First, let’s create the basic HTML structure for our age calculator app. We will use HTML and CSS to design the app before adding JavaScript functionality. Open your preferred code editor, such as Visual Studio Code, and create a new HTML file. Add the necessary code for the structure, including the title of the webpage and the channel name.

Next, we will add the CSS styles to customize the appearance of our app. We will define styles for the container and calculator divs, as well as the title, input box, and button. These styles will determine the width, height, background, font size, and other visual aspects of the app.

Once the HTML structure and CSS styles are in place, you can preview the app in a web browser. Use a code editor extension like Live Server to automatically refresh the webpage whenever you make changes to the code.

Adding Functionality with JavaScript

Now it’s time to add the JavaScript functionality that will enable the age calculator app to work. We will use JavaScript to calculate and display the user’s age based on their selected date of birth.

First, we need to create an input box with a date picker and a button. The date picker allows the user to select their birthdate, and the button triggers the age calculation. We will add CSS styles to make the date picker work when clicked anywhere, not just on the calendar icon.

Next, we will write JavaScript code to handle the input and perform the calculations. We will store the user’s selected birthdate in a variable called birthDate. Then, we will calculate the current date and extract the day, month, and year. Using these values, we will determine the difference in years, months, and days between the birthdate and current date.

To handle certain conditions, such as the current month being earlier than the birth month, we will use conditional statements and additional functions. These functions will help us calculate the exact number of days in each month and adjust the month and year values accordingly.

Finally, we will display the calculated age on the webpage using JavaScript. We will assign the calculated values to variables representing the day, month, and year differences. Then, we will update the HTML elements with these values to show the user’s age on the app.


In this tutorial, you have learned how to build an age calculator app using HTML, CSS, and JavaScript. We walked you through the step-by-step process of creating the app’s HTML structure, adding CSS styles for customization, and implementing the JavaScript functionality for age calculation. This small project can be a valuable addition to your portfolio. Feel free to modify the code and customize the design to make it your own. Happy coding!

Remember that this age calculator app is just a small example of what you can achieve with HTML, CSS, and JavaScript. There are countless possibilities for building interactive web applications using these technologies. So keep exploring and experimenting to enhance your coding skills further.