mortage calculator in php wrong amount

Question

i am working on a simple loan calculator, so simple that it's not even working properly.

function calculatePayment($price, $down, $term)
{
    $loan = $price - $down;
    $rate = (4/100) / 12;
    $month = $term * 12;
    $payment = floor(($loan*$rate/1-pow(1+$rate,(-1*$month)))*100)/100;
    return $payment;
}

echo calculatePayment(200000,0,30);

this output: 666.36

that would be great if the monthly loan payement is this (not that is the 666 number but low number hahah), my problem is this be higher.

why am i getting the this?

Answer 1

I just added put (1-pow(1+$rate,(-1*$month))) this because what is happening here is that $loan*$rate will be divided on 1 only then continue

function calculatePayment($price, $down, $term)
{
$loan = $price - $down;
$rate = (4/100) / 12;
$month = $term * 12;
$payment = floor(($loan*$rate/(1-pow(1+$rate,(-1*$month))))*100)/100;
return $payment;
}

echo calculatePayment(200000,0,30);

The answer is 954.83