Amortization Schedule Example -- PHP Version

Amortization.php

<?php 
	/**
	 * AMORTIZATION CALCULATOR
	 * @author PRANEETH NIDARSHAN
	 * @version V1.0
	 */
	class Amortization
	{
		private $loan_amount;
		private $term_years;
		private $interest;
		private $terms;
		private $period;
		private $currency = "XXX";
		private $principal;
		private $balance;
		private $term_pay;

		public function __construct($data)
		{
			if($this->validate($data)) {

				
				$this->loan_amount 	= (float) $data['loan_amount'];
				$this->term_years 	= (int) $data['term_years'];
				$this->interest 	= (float) $data['interest'];
				$this->terms 		= (int) $data['terms'];
				
				$this->terms = ($this->terms == 0) ? 1 : $this->terms;

				$this->period = $this->terms * $this->term_years;
				$this->interest = ($this->interest/100) / $this->terms;

				$results = array(
					'inputs' => $data,
					'summary' => $this->getSummary(),
					'schedule' => $this->getSchedule(),
					);

				$this->getJSON($results);
			}
		}

		private function validate($data) {
			$data_format = array(
				'loan_amount' 	=> 0,
				'term_years' 	=> 0,
				'interest' 		=> 0,
				'terms' 		=> 0
				);

			$validate_data = array_diff_key($data_format,$data);
			
			if(empty($validate_data)) {
				return true;
			}else{
				echo "<div style='background-color:#ccc;padding:0.5em;'>";
				echo '<p style="color:red;margin:0.5em 0em;font-weight:bold;background-color:#fff;padding:0.2em;">Missing Values</p>';
				foreach ($validate_data as $key => $value) {
					echo ":: Value <b>$key</b> is missing.<br>";
				}
				echo "</div>";
				return false;
			}
		}

		private function calculate()
		{
			$deno = 1 - 1 / pow((1+ $this->interest),$this->period);

			$this->term_pay = ($this->loan_amount * $this->interest) / $deno;
			$interest = $this->loan_amount * $this->interest;

			$this->principal = $this->term_pay - $interest;
			$this->balance = $this->loan_amount - $this->principal;

			return array (
				'payment' 	=> $this->term_pay,
				'interest' 	=> $interest,
				'principal' => $this->principal,
				'balance' 	=> $this->balance
				);
		}

		public function getSummary()
		{
			$this->calculate();
			$total_pay = $this->term_pay *  $this->period;
			$total_interest = $total_pay - $this->loan_amount;

			return array (
				'total_pay' => $total_pay,
				'total_interest' => $total_interest,
				);
		}

		public function getSchedule ()
		{
			$schedule = array();
			
			while  ($this->balance >= 0) { 
				array_push($schedule, $this->calculate());
				$this->loan_amount = $this->balance;
				$this->period--;
			}

			return $schedule;

		}

		private function getJSON($data)
		{
			header('Content-Type: application/json');
			echo json_encode($data);
		}
	}

	$data = array(
		'loan_amount' 	=> 20000,
		'term_years' 	=> 1,
		'interest' 		=> 10,
		'terms' 		=> 12
		);

	$amortization = new Amortization($data);


	?>

As a kind gesture, I noticed a typo in this post getShedule should be getSchedule, and therefore also 'shedule' => $this->getShedule(), should be 'schedule' => $this->getSchedule(),.

Thank you very much for sharing!

Thank you very much for the suggestion :-)

Can you tell us how we can show in our table? I mean how can we parse?

If you are using only PHP (no Ajax) to show the Amortization schedule you can just run a for or foreach loop as below,

<?php

$schedule = $amortization['schedule'];

?>

<table>
    <thead>
        <tr>
            <th>Payment</th>
            <th>Interest</th>
            <th>Principal</th>
            <th>Balance</th>
        </tr>
    </thead>
    <tbody>
        <?php foreach($schedule as $term_detail): ?>
        <tr>
            <td><?= $term_detail['payment'] ?></td>
            <td><?= $term_detail['interest'] ?></td>
            <td><?= $term_detail['principal'] ?></td>
            <td><?= $term_detail['balance'] ?></td>
        </tr>
        <?php endforeach; ?>
    </tbody>
</table>

It will populate a table for you. If you are using Ajax you can use JavaScript to do the same thing.

A very nice script. Thumbs up. My question is, how can we loop the dates for the payments, let's assume we also pass the start date of the loan and maybe the loan years is 1, so this means loan repayment dates are 12. How can we loop through these dates so that we can capture the dates in the schedule?

good work, but some time no result shown. i.e. if interest=2.5 or 7.5 or 12 or 12.5 or 14
$data = array(
'loan_amount' => 20000,
'term_years' => 1,
'interest' => 7.5,
'terms' => 12,
);
$amortization = new Amortization($data);

good work, but some time no result shown. i.e. if interest=2.5 or 7.5 or 12 or 12.5 or 14
$data = array(
'loan_amount' => 20000,
'term_years' => 1,
'interest' => 7.5,
'terms' => 12,
);
$amortization = new Amortization($data);

The calculations give a balance greater than 0.
Solved this by changing the loop to work with the term instead of the balance. Like

$i = 1;
while ($i <= $this->terms) {
    array_push($schedule, $this->calculate());
    $this->loan_amount = $this->balance;
    $this->period--;
    $i++;
}

How can I rewrite this using vanilla php? Am looking for this kind of solution for the last 1 week now.

How can I rewrite this using vanilla php? Am looking for this kind of solution for the last 1 week now.

What do you mean vanilla php? the script is php only.