Calculate exact age from birthdate (with 1/2)

Question

I'm trying to determine a users exact age, calculated off their birthdate.

I need to be able to tell if they are 1/2 through their current year or not.

Example:

• 08/17/1983 -> 29 1/2
• 05/21/1983 -> 30

Here's what I currently use for the age calculation function:

$birthday = new DateTime($birthday);
$interval = $birthday->diff(new DateTime);
$age = $interval->y;

Thanks!

Answer 1

Seems like you could just test the m part of the interval.

if ($interval->m >= 6 ) {
    // it's $age + 1/2
}

Answer 2

Calculate the exact months in your interval, then divide by 6, truncate, then divide by 2.

/6 + truncate + /2 is like /12 with .0 or .5 only .

<?php 

$birthday = new DateTime('08/17/1983');
$interval = $birthday->diff(new DateTime);
$age = floor((($interval->y * 12) + $interval->m) / 6) / 2;

//To display with floating point
echo $age;

echo '<br />';

//To display with "1/2"
echo floor($age) . (fmod($age, 1) == 0.5 ? ' 1/2' : '');

?>

Result: 29.5 and 29 1/2

Demo: http://phpfiddle.org/main/code/m7c-uck