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<?php
declare(strict_types = 1);
namespace Kauri\Loan\PaymentAmountCalculator;
use Kauri\Loan\PaymentAmountCalculatorInterface;
class AnnuityPaymentAmountCalculator implements PaymentAmountCalculatorInterface
{
/**
* @see http://www.financeformulas.net/Annuity_Payment_Formula.html
* @see http://www.tvmcalcs.com/index.php/calculators/apps/lease_payments
* @see http://www.ms.uky.edu/~rkremer/files/Finance04.pdf
* @param array $periods
* @param float $presentValue
* @param float $interestRate
* @param float $futureValue
* @return array
*/
public function getPaymentAmounts(
array $periods,
float $presentValue,
float $interestRate,
float $futureValue = 0.0
): array {
$paymentAmounts = array();
$discountFactor = 0;
$futureValueDenominator = 1;
foreach ($periods as $sequenceNo => $periodsLength) {
$partialDiscountFactor = pow(1 + ($interestRate / 360 / 100 * $periodsLength),
-$sequenceNo);
$discountFactor = $discountFactor + $partialDiscountFactor;
$partialFutureValueDenominator = 1 + ($interestRate / 360 / 100 * $periodsLength);
$futureValueDenominator = $futureValueDenominator * $partialFutureValueDenominator;
}
$paymentAmount = ($presentValue - ($futureValue / $futureValueDenominator)) / $discountFactor;
$paymentAmounts[$sequenceNo] = $paymentAmount;
return $paymentAmounts;
kaurikk /
loan-amount-calculator
