<?php
 
error_reporting(-1);
 
function getSum ($percent, $tax, $account, $creditSum, $payout) {
	$paymentTotal = 0;
	$creditSum = $creditSum + $account;
	if (($creditSum * ($percent - 1) + $tax) >=  $payout) {
		$paymentTotal = 'Бесконечно';
		}
		else {
			for ( ; ; ) {
				$creditBalance = $creditSum * $percent - $payout + $tax;
				$paymentTotal +=  $payout;
				$creditSum = $creditBalance;
				if ($creditBalance < 0) {
					$paymentTotal += $creditBalance;
					$paymentTotal = round($paymentTotal,2);
					break;
			}
		}
	}
	return $paymentTotal;
}
$creditSum = 39999;
$payout = 5000;
 
$homoCreditBank = getSum (1.04, 500, 0, $creditSum, $payout);
$softBank = getSum (1.03, 1000, 0, $creditSum, $payout);
$StrawberryBankTotal = getSum (1.02, 0, 7777, $creditSum, $payout);
 
echo "homoCreditBank $homoCreditBank руб \n";
echo "SoftBank $softBank руб \n";
echo "StrawberryBankTotal $StrawberryBankTotal руб \n";