PHP: Excel PMT

The Microsoft Excel PMT function calculates the payment for a loan based on constant payments and a constant interest rate. Syntax: PMT(rate, nper, pv, fv, type).

• Rate is the interest rate for the loan
• Nper is the total number of payments for the loan
• Pv is the present value, or the total amount that a series of future payments is worth now
• Fv is the future value, or a cash balance you want to attain after the last payment is made. If fv is omitted, it is assumed to be 0 (zero), that is, the future value of a loan is 0
• Type is the number 0 (zero) or 1 and indicates when payments are due
  • 0 or omitted At the end of the period
  • 1 At the beginning of the period

/**
 * This is the PHP version of the PMT function used in Excel
 *  
 * @param float $rate
 * @param int $nper
 * @param float $pv
 * @param float $fv
 * @param int $type
 * @return float
 */
function PMT($rate = 0, $nper = 0, $pv = 0, $fv = 0, $type = 0) {
	if ($rate > 0) {
		return (-$fv - $pv * pow(1 + $rate, $nper)) / (1 + $rate * $type) / ((pow(1 + $rate, $nper) - 1) / $rate);
	} else {
		return (-$pv - $fv) / $nper;
	}
}
 
$rate = 10 / 1200; // rate = 10%
$nper = 60; // months
$pv   = 1000;
$fv   = 200;
 
$payment = round(PMT($rate, $nper, -$pv, $fv));