<?php 

error_reporting(-1);

function computeProfitableCredit($percent, $commission, $firstPaymentPrice,$payout,$creditBalance) {
	$total = 0;
	$creditBalance = $creditBalance + $firstPaymentPrice;
	for ($month = 1;$month <= 30;$month++) {
		$variable = ($creditBalance * $percent) + $comission;
		if ($variable >= 5000 ) {
			$creditBalance = ($creditBalance * $percent) + $comission - $payout;
			$paymentTotal = $paymentTotal + $payout;
		}
		elseif ($variable < 5000) {
			if ($creditBalance > 0) {
				$creditBalance = $total + $firstPaymentPrice - $variable;
				$paymentTotal = $paymentTotal + $variable;
			}
		}
	}
	return $paymentTotal;
}

$creditSum = 39999;
$payout = 5000;

$homoCreditPercent = 1.04;
$homoCreditComission = 500;
$homoCreditFirstPaymentPrice = 0;

$softbankPercent = 1.03;
$softbankComission = 1000;
$softbankFirstPaymentPrice = 0;

$strawberryBankPercent = 1.02;
$strawberryBankComission = 0;
$strawberryBankFirstPaymentPrice = 7777;

$homoCreditTotal = computeProfitableCredit($homoCreditPercent,$homoCreditComission,$homoCreditFirstPaymentPrice,$payout,$creditSum);
$softbankTotal = computeProfitableCredit($softbankPercent,$softbankComission,$softbankFirstPaymentPrice,$payout,$creditSum);
$strawberryBankTotal = computeProfitableCredit($strawberryBankPercent,$strawberryBankComission,$strawberryBankFirstPaymentPrice,$payout,$creditSum);

echo "В банке homoCredit нужно заплатить {$homoCreditTotal} рублей\n";
echo "В банке softbank нужно заплатить {$softbankTotal} рублей\n";
echo "В банке strawberryBank нужно заплатить {$strawberryBankTotal} рублей\n";