<?php

function calculateCredit($servicePayment, $percent) {

    global $creditBalance, $monthlyPayment;
    static $paymentTotal = 0;
 
    for ($month = 1; $month <= 120; $month++) {

        $creditBalance = $creditBalance * $percent + $servicePayment;

    	if ($creditBalance - $monthlyPayment < 0) {
    		$paymentTotal += $creditBalance;
    		$creditBalance = 0;
    		break;
    	}

        $creditBalance -= $monthlyPayment;
        $paymentTotal += $monthlyPayment;

    }

    return $paymentTotal;

}

$creditBalance = 39999;
$monthlyPayment = 5000;

$homoCreditTotal = calculateCredit(500, 1.04); //кредит за 4% и 500 р комиссии в месяц
$softBankTotal = calculateCredit(1000, 1.03); //кредит за 3% и 1000 р комиссии в месяц
$strawberryBankTotal = calculateCredit(0, 1.02) + 7777; // 2% в месяц, без комиссии, но с платой в размере 7777 р за открытие счета

echo "HomoCredit: {$homoCreditTotal}\n";
echo "SoftBank: {$softBankTotal}\n";
echo "StrawberryBank: {$strawberryBankTotal}\n";