(PHP 4 >= 4.2.0, PHP 5, PHP 7, PHP 8)
fmod — Returns the floating point remainder (modulo) of the division of the arguments
   Returns the floating point remainder of dividing the dividend
   (num1) by the divisor (num2).
   The remainder (r) is defined as: num1 = i * num2 + r, for 
   some integer i. If num2 is
   non-zero, r has the same sign as
   num1 and a magnitude less than the magnitude of
   num2.
  
num1The dividend
num2The divisor
   The floating point remainder of 
   num1/num2
  
Example #1 Using fmod()
<?php
$x = 5.7;
$y = 1.3;
$r = fmod($x, $y);
// $r equals 0.5, because 4 * 1.3 + 0.5 = 5.7
var_dump($x, $y, $r);
?>