Age Calculator | HTML, CSS & JavaScript

Age Calculator with HTML, CSS & JavaScript

30 DAYS 30 PROJECT CHALLENGE

Day #18

Project Overview

An Age Calculator built using HTML, CSS, and JavaScript that calculates a user’s exact age based on their date of birth.
The application computes age in years, months, and days, validates user input, and displays results instantly with a clean and user-friendly interface.

Key Features

Calculates age in years, months, and days accurately.
Date of birth selection using a date picker.
Validates input to prevent empty or future dates.
Displays results instantly without page reload.
Clean, responsive, and easy-to-use design.
Suitable for learning date manipulation in JavaScript.

HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0"/>
  <title>Age Calculator</title>
  <link rel="stylesheet" href="style.css" />
</head>
<body>

  <div class="calculator">
    <h2>Age Calculator</h2>

    <label for="dob">Select your Date of Birth</label>
    <input type="date" id="dob" />

    <button onclick="calculateAge()">Calculate Age</button>

    <div class="result" id="result"></div>
  </div>

  <script src="script.js"></script>
</body>
</html>

CSS Code

* {
  box-sizing: border-box;
  font-family: "Segoe UI", sans-serif;
}

body {
  min-height: 100vh;
  background: #042453; /* DO NOT CHANGE */
  display: flex;
  justify-content: center;
  align-items: center;
}

.calculator {
  background: #ffffff;
  width: 320px;
  padding: 25px;
  border-radius: 12px;
  text-align: center;
  box-shadow: 0 15px 30px rgba(0,0,0,0.2);
}

h2 {
  margin-bottom: 15px;
}

label {
  font-size: 14px;
}

input {
  width: 100%;
  padding: 10px;
  margin: 10px 0;
  border-radius: 6px;
  border: 1px solid #ccc;
}

button {
  width: 100%;
  padding: 10px;
  border: none;
  border-radius: 6px;
  background: #4f46e5;
  color: white;
  cursor: pointer;
}

.result {
  margin-top: 15px;
  font-size: 14px;
  font-weight: 600;
}

Javascript Code

function calculateAge() {
  const dobInput = document.getElementById("dob").value;
  const result = document.getElementById("result");

  if (!dobInput) {
    result.style.color = "red";
    result.innerText = "Please select your date of birth";
    return;
  }

  const dob = new Date(dobInput);
  const today = new Date();

  if (dob > today) {
    result.style.color = "red";
    result.innerText = "Date of birth cannot be in the future";
    return;
  }

  let years = today.getFullYear() - dob.getFullYear();
  let months = today.getMonth() - dob.getMonth();
  let days = today.getDate() - dob.getDate();

  if (days < 0) {
    months--;
    days += new Date(today.getFullYear(), today.getMonth(), 0).getDate();
  }

  if (months < 0) {
    years--;
    months += 12;
  }

  result.style.color = "green";
  result.innerText = `You are ${years} years, ${months} months, and ${days} days old.`;
}