<?php

error_reporting(-1);

function countBenefit($sumOfCredit, $percentage, $commission, $payment, $entryPayment)
{
$paymentTotal = 0;
if ($entryPayment) {
        $sumOfCredit += $entryPayment;
}
for ($sumOfCredit += ($sumOfCredit * $percentage); $sumOfCredit > 0; $sumOfCredit += ($sumOfCredit * $percentage)
) {
        if ($sumOfCredit > ($payment - $commission)) {
        $sumOfCredit -= ($payment - $commission);
        $paymentTotal += $payment;
        }
        else {
                $payment = $sumOfCredit;
                $paymentTotal += $payment;
                $sumOfCredit -= $payment;
        }
}
return $paymentTotal;
}

$homoBank = countBenefit(39999, 0.04, 500, 5000, 0);
$softBank = countBenefit(39999, 0.03, 1000, 5000, 0);
$strawBerry = countBenefit(39999, 0.02, 0, 5000, 7777);

echo $homoBank;
echo "<br>";
echo $softBank;
echo "<br>";
echo $strawBerry; // Самый выгодный
