<?php

error_reporting(-1);

function pay($creditSum, $payout, $percent, $servicePay, $opening) {
	$creditSum = $creditSum + $opening;
	for ($i = 0; $i < 30; $i++) {
		if ($creditSum <= $payout) {
			$paymentTotal = $paymentTotal + $creditSum;
			break;
		} else {
			$creditSum = ($creditSum / 100 * (100 + $percent)) + $servicePay - $payout;
		    $paymentTotal = $paymentTotal + $payout;
		}
	}
	return $paymentTotal;
}

$creditSum  = 40000;
$payout = 5000;

$homoCredit = pay($creditSum, $payout, 4, 500, 0);
$softbank = pay($creditSum, $payout, 3, 1000, 0);
$strawberryBank = pay($creditSum, $payout, 2, 0, 7777);

echo "homoCredit: {$homoCredit} руб.\n";
echo "softbank: {$softbank} руб.\n";
echo "strawberryBank: {$strawberryBank} руб.\n";