<?php

error_reporting(-1);

$creditBalance = 1000;
$percent = 1.03;
$servicePayment = 1000;
$monthlyPayment = 5000;
$paymentTotal = 0;

for ($month = 1; $month <= 20; $month ++) {
	
	$creditBalance = ( $creditBalance * $percent ) + $servicePayment; 		/*  - $monthlyPayment */
	$paymentTotal = $paymentTotal + $monthlyPayment;
	$obligation = $creditBalance - $paymentTotal;
	echo "{$month} месяц спустя:\n сумма долга = {$creditBalance} руб;\n выплачено всего - {$paymentTotal} руб.; \n обязательство $obligation\n \n";
	
	if ($obligation <= $monthlyPayment) {
		
		$lastPay = $monthlyPayment - ($monthlyPayment - $obligation);
		$paymentTotal = $paymentTotal + $lastPay;
		
		/* $obligation = $obligation - $lastpay; */
		
	 	$obligation = $creditBalance - $paymentTotal;
		
		echo "последний платёж - $lastPay, ";
		$obligation = $creditBalance - $paymentTotal;
		echo "обязательство $obligation";
		break;
	}
	
	}