<?php
error_reporting(-1);

$credit = 40000;
$percent = 1.03;
$service = 1000;
$monthlyPayment = 5000;
$totalPayment = 0;

for ($month = 1; $month <=20; $month ++) {
	if ($credit == 0) {
		echo "Оплачено!!";
		break;
	}
     $credit = ($credit * $percent) + $service;
     
     if ($credit < 5000) {
     	$monthlyPayment = $credit;
     }
     $credit = $credit - $monthlyPayment;
     $totalPayment = $totalPayment + $monthlyPayment;
     echo "На $month-й месяц, сумма долга $credit , всего оплачено $totalPayment \n";
}
?>