(PHP 4 >= 4.2.0, PHP 5, PHP 7, PHP 8)
fmod — Returns the floating point remainder (modulo) of the division of the arguments
$num1, float $num2): float
   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
?>