(PHP 4 >= 4.2.0, PHP 5)

fmod -- Returns the floating point remainder (modulo) of the division of the arguments
Description
float fmod ( float x, float y )


Returns the floating point remainder of dividing the dividend (x) by the divisor (y). The reminder (r) is defined as: x = i * y + r, for some integer i. If y is non-zero, r has the same sign as x and a magnitude less than the magnitude of y. 

Example 1. Using fmod()

<?php
$x = 5.7;
$y = 1.3;
$r = fmod($x, $y);
// $r equals 0.5, because 4 * 1.3 + 0.5 = 5.7
?>