PHP How to create a counter from for loop

Try this:

$z = 0;
for ($x=9; $x<=12; $x++) {
  for ($y=1; $y<=31; $y++) {
    echo $y.'<br>';
    $z++;
  }
}

echo $z;

Add another variable and just count it up.

Unless I'm misunderstanding what you want:

$counter = 0;//declare your counter here
for ($x=9; $x<=12; $x++) {
  for ($y=1; $y<=31; $y++) {
    echo $y.'<br/>';//The '$y' variable only exists inside this 'scope'. That is why counter must be declared BEFORE the for-loop.
    $counter++;//Add one for each time it goes through this loop.
  }
}
echo $counter;

I think the piece of understanding that you need is about 'scope'. Loosely, anything you see with brackets ({ }) is probably a new scope, or context. Scopes can generally see the scopes that declared them, but cannot see into scopes they declare. Thus, in the above example, the largest scope is where $counter is declared, but it cannot see the $y variable because it is declared in an internal scope.

//This is the 'outer scope'
$counter = 0;//Any scopes internal to this can see this variable.
for ($x=9; $x<=12; $x++) {//This declares a new scope internal to the outer scope. It can see $counter but not $y.
  for ($y=1; $y<=31; $y++) {//This declares a new scope internal to both other scopes. It can see $x and $counter.
    echo $y.'<br/>';
    $counter++;
  }
  //Note that here we can 'see' $counter and $x, but not $y, even though $y has been declared.
  //This is because when we leave the internal for loop it's 'scope' and any variables associated
  //are discarded and no longer accessible.
}
echo $counter;//At this point only the counter variable is still around, because it was declared by this scope.

Just create a counter variable and increment it in the loop:

$counter = 0;
for ($x=9; $x<=12; $x++) {
  for ($y=1; $y<=31; $y++) {
    echo $y.'<br>';
    ////// Now it run good but i want add $y into number 
    ///// I know that this loop total run 124 time  so i want 124 
    $counter++;
  }
}
echo $counter;