How to Calculate Age Based on Date of Birth in Code

Calculating a user's age from their date of birth is a common programming task. In PHP, there are multiple methods to achieve this:

Using Object-Oriented DateTime Class (PHP >= 5.3.0)

// Instantiate a DateTime object for the birth date
$birthDate = new DateTime('1999-03-15');

// Instantiate a DateTime object for the current date
$currentDate = new DateTime('now');

// Calculate the difference between the two dates in years
$age = $currentDate->diff($birthDate)->y;

// Output the age
echo $age;

Using Procedural Date Functions (PHP >= 5.3.0)

// Calculate the difference between the dates using date_diff()
$age = date_diff(date_create('1999-03-15'), date_create('now'))->y;

// Output the age
echo $age;

Using MySQL Query (MySQL >= 5.0.0)

If the date of birth is stored in a MySQL database, the following query can be used to calculate the age:

SELECT TIMESTAMPDIFF(YEAR, '1999-03-15', CURDATE()) AS age;

This query calculates the difference between the specified date and the current date in years and returns it as the age column.