phpeveryday.com

<?php
$start = (float) array_sum(explode(' ',microtime()));

// put you code that wanted to render at here


$end = (float) array_sum(explode(' ',microtime()));

echo "Processing time: ". sprintf("%.4f", ($end-$start))." seconds";
?>

PHP's microtime() return current UNIX timestamp in microseconds. We compare start and end. The difference between the two is the time taken for script execution.