<?php

/**
 * Calculates monthly or total payable amount of the loan.
 *
 * @param integer $amount Loaned amount, default is 1000
 * @param integer $percent Percent in which amount should be calculated, default is 15
 * @param integer $months Loan duration in months, default is 12 months (1 year)
 * @param boolean $total If positive value is passed function returns total payable amount instead of monthly
 * @return float Returns 2 decimal float number
 */
function calculate_loan($amount = 1000, $percent = 15, $months = 12, $total = FALSE)
{
    $rate = 1 - (1 / pow((1 + $percent / 1200), $months));
    $monthly = $amount * (($percent / 12) / 100) / $rate;
    $total AND $monthly *= $months;
    return round($monthly, 2);
}

echo calculate_loan(1000, 15, 12);