How to correctly format a monetary value?

Remove the point and the R $.

<?php

$moeda = "R$ 1.500,95";

// Com str_replace (Remove a string 'R$ ' e '.'
$valor = str_replace( array('R$ ', '.'),  '', $moeda);
echo $valor; //1550,95

// Com preg_replace (Remove tudo que for diferente de dígito e vírgula)
$valor = preg_replace( '/([^\d,])/',  '', $moeda);
$valor = preg_replace('/[,]+/', ',', $valor); // Fix para caso seja passado mais de 1 ","
echo $valor; //1550,95

?>

Another solution would be to remove only keep the integers and divide them by 100.

$moeda = 'R$ 1.550,52';

$valor = preg_replace('/[^0-9]/', '', $moeda);    
$valor = bcdiv($valor, 100, 2);
$valor = strtr($valor, '.', ',');

echo $valor;

Result:

  

1550.52

In this way, this would become:

string : 0e100 => 1,00
double : 0e100 => 0,00
string : 0x98 => 0,98
integer : 0x98 => 1,52
string : R$ 100.00 => 100,00
integer : 10000 => 100,00
double : 100.00 => 1,00
integer : 12345 => 123,45
string : 123.45 => 123,45
double : 123.45 => 123,45
string : 1a2b3c4d5e => 123,45
string : 123,45 => 123,45
string : R$ 123,45 => 123,45
string : 1 => 0,01
integer : 1 => 0,01

double : 9.0E+99 => 8999999999999999948859130765266355329578537025198862586562510896759102769772101980841694466750283776,00
integer : 9223372036854775807 => 92233720368547758,07

Try this.

This function, as it is, has " problems " with float , I do not recommend using float / double. The float of 100.00 will be 1,00 and 100.01 will become 100,01 , ie the 100.00 will not go to 100,00 , which may not be expected.

Obviously, impersonation must contain the cents , if it is just R$ 1.550 will move to 15,50 . However, informing 1.550,00 will not have problem, as will 155000 or even 1a550b00 .

You can use the function preg_replace or str_replace , see below with preg_replace :

echo preg_replace('/^[0-9,]/', '', $valor);
// Saída: 1500,95