<?php

error_reporting(-1);

function calcPayment($creditSum, 
					 $percent, 
					 $servicePayment, 
					 $monthlyPayment, 
					 $openPayment){
	$paymentTotal = 0;
	for($month = 1; $creditSum > 0; $month++){
		$creditSum = $creditSum * $percent + $servicePayment;
		if ($creditSum <= $monthlyPayment) {
			$paymentTotal += $creditSum;
			$creditSum = 0;
		} else {
			$creditSum -= $monthlyPayment;
			$paymentTotal = $paymentTotal + $monthlyPayment;
		}
	}
	$paymentTotal = $paymentTotal + $openPayment;
	return $paymentTotal;
}
$creditSum = 39999;
$payout = 5000;
$homoCreditTotal = round(calcPayment($creditSum, 1.04, 500, $payout, 0),2);
$softbankTotal = round(calcPayment($creditSum, 1.03, 1000, $payout, 0),2);
$strawberryBankTotal = round(calcPayment($creditSum, 1.02, 0, $payout, 7777),2);

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

$bankOffer = ['homoCredit' => $homoCreditTotal, 'softbank' => $softbankTotal, 'strawberryBank' => $strawberryBankTotal];
asort($bankOffer);
$bank = array_keys($bankOffer);
echo "\nНаиболее выгодное предложение от {$bank[0]}\n";