<?php

error_reporting(-1);

function countcredits($bankpercent, $service) {
    $credit = 39999;
    $payPerMonth = 5000;
    $payed = 0;
for ($i = 1; $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;
}
}   return $payed;
}

$homoCreditsumm = countcredits(1.04, 500);
$softBanksumm = countcredits(1.03, 1000);
$strawberryBanksumm = countcredits(1.02, 0) + 7777; /* 7777 руб. - за открытие счета */

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