<?php

error_reporting(-1);

function getCreditTotal($creditSum, $percent, $comission, $payout, $paymentTotal) {
	for ($month = 1; $month < 20; $month ++) {
		
		$creditSum = ( $creditSum * $percent ) + $comission - $payout;
		$paymentTotal = $paymentTotal + $payout;
	    
	    if ($creditSum < 0) {
	    	break;
	    }	elseif ($creditSum < 4000) {
	    	$creditSum = ( $creditSum * $percent ) + $comission;
	    	$paymentTotal = $paymentTotal + $creditSum;
	    	$creditSum = $creditSum - $creditSum;
	    	echo "{$month} месяц спустя: долг = {$creditSum} руб, выплачено всего {$paymentTotal} руб. \n";
	    	break;
	    	}
	}
	
	return $paymentTotal;
}
$creditSum = 40000;
$payout = 5000;
$homoCreditTotal = getCreditTotal($creditSum, 1.04, 500, $payout, 0);
$softBankTotal = getCreditTotal($creditSum, 1.03, 1000, $payout, 0);
$strawberryBankTotal = getCreditTotal($creditSum, 1.02, 0, $payout, 0) + 7777;
echo "homoCredit:{$homoCreditTotal}\nsoftBank:{$softBankTotal}\nstrawberryBank:{$strawberryBankTotal}";