<?php

error_reporting(-1);

function countcredits($bankpercent, $service) {
            $credit = 39999;
            $payPerMonth = 5000;
            $payed = 0;
    for ($i = 0; $credit > 0; $i++) {
        $creditmonthly = $credit * $bankpercent + $service;
    if ($creditmonthly > $payPerMonth) {
        $credit = $creditmonthly - $payPerMonth;
        $payed = $payPerMonth + $payed;
    } elseif ($creditmonthly < $payPerMonth) {
        $credit = $creditmonthly - $creditmonthly;
        $payed = $payed + $creditmonthly;
            }
        }
}

$homoCreditsumm = countcredits(1.04, 500);
$softBanksumm = countcredits(1.03, 1000);

echo "homocredit: {$homoCreditsumm} руб.\n";
echo "sofBank: {$softBanksumm} руб.\n";