Amortization Script - php

Question

I am trying to create an amortization calculator that calculates the declining principal
$x = 1;
$starting_pmt = 26;
$ending_pmt = 36;
$i = 0.0010316264327892;
$p = 410000;
$pmt = 916.84;
$num_pmts = $ending_pmt - $starting_pmt;
echo "<table border=\"1\" align=\"center\">";
echo "<tr><th>PMT Num</th>";
echo "<th>Balance</th>";
echo "<th>Principle</th>";
echo "<th>TTL Principle</th>";
echo "<th>Interest</th>";
echo "<th>Payment</th>";
echo "</tr>";
while ( $starting_pmt <= $ending_pmt ) {
echo "<tr><td>";
echo $starting_pmt;
echo "</td><td>";
echo $p;
echo "</td>";
echo "<td>$prin</td>";
echo "<td>$TTLprin</td>";
echo "<td>$interest</td>";
echo "<td>$TTLPmt</td> </tr>";
$starting_pmt = $starting_pmt + 1;
$p = $p -($p*$i);
$prin = $pmt - ($p * $i);
$interest = $pmt - $prin;
$TTLPmt = $prin + $interest;
//$cumTTL = $$pmt - ($p * $i);
$TTLprin = $prin + $prin;
}
echo "</table>";
?>
balance for each payment and the total principle paid between two values. I also want to calculate the interested paid for each payment and the accumulative interest paid between the two values.
This is what I am starting with.
I cannot figure out how to get the loop to do the math during each iteration............... I have been working my original code and I am getting closer. I cannot get the loop to calculate the cumulative total for principal and interest paid.
<?php
$starting_pmt = 1;
$ending_pmt = 10;
$i = 0.0010316264327892;
$p = 410000;
$pmt = 916.84;
$num_pmts = $ending_pmt - $starting_pmt;
while($x < $num_pmts) {
echo "<tr>";
echo "<td>$x</td>";
echo "<td>".$p - ($p*$i)."</td>";
echo "<td></td>";
echo "<td></td>";
echo "<tr>";
$x++;
I get the math. It's getting the while loop to do what I need. It's not calculating the cumulative total for the principle paid.

Answer 1

Here is a way to make an amortization script, you need to pass back what you want your rate, payment date, and all that good stuff. then I am returning an associative array with all the values for each month.
public static function amortizeLoan($principal, $rate, $term, $extra_days, $payment_date){
$payment = self::getPayment($principal,($rate*100),$term,$extra_days);
$MonthlyInterestRate = $rate / 12;
$Multiplier = 1 + $MonthlyInterestRate;
$TermRate = 1;
for($x=0;$x<$term;$x++){
$TermRate = $TermRate * $Multiplier;
}
$Days = $extra_days - 30;
$oddDayInt = $Days > 0 ? round($principal * ($rate / 365.25) * $Days,2) : 0;
$amortization = [];
$total_interest = 0;
$total_principal = 0;
$remaining_principal = $principal;
$compareDay = date('d', strtotime($payment_date));
for($x=0;$x<$term;$x++){
$this_int_paid = round((($rate)/12) * $remaining_principal,2);
if($x==0){$this_int_paid += $oddDayInt;}
$this_princ_paid = round($payment - $this_int_paid,2);
$this_rem_princ = round($remaining_principal - $this_princ_paid,2);
if($x == ($term-1)){
if($this_rem_princ < 0){
$this_princ_paid-=abs($this_rem_princ);
$payment=round($this_int_paid+$this_princ_paid,2);
}else{
$this_princ_paid+=$this_rem_princ;
$payment=round($this_int_paid+$this_princ_paid,2);
}
}
$remaining_principal -= $this_princ_paid;
$total_interest += $this_int_paid;
$total_principal += $this_princ_paid;
// *** If month days < payment date, payment date falls on the last day of that month.***
$nextMonth = strtotime("last day of next month", strtotime($payment_date));
$lastDayNextMonth = date('d', $nextMonth);
if ($compareDay >= $lastDayNextMonth) {
$payment_date_time = $x ? $nextMonth : strtotime($payment_date);
} else {
$payment_date_time = $x ? strtotime("+1 month", strtotime($payment_date)) : strtotime($payment_date);
}
if ($lastDayNextMonth > date('d', strtotime($payment_date)) && date('t', strtotime($payment_date)) < $compareDay) {
$date = date('Y-m-d', $nextMonth);
$newDate = date_create($date);
$newDate->format('Y-m-d');
$finalDate = date_date_set(
$newDate,
date_format($newDate, 'Y'),
date_format($newDate, 'm'),
$compareDay
);
$formatedDate = $finalDate->format('m/d/y');
$payment_date_time = strtotime($formatedDate);
}
$payment_date = gmdate("Y-m-d", $payment_date_time);
$amortization[] = [
"payment"=>($x+1),
"amount"=>$payment,
"principal"=>$this_princ_paid,
"interest"=>$this_int_paid,
"total_principal"=>$total_principal,
"total_interest"=>$total_interest,
"remaining_balance"=>round($remaining_principal,2),
"payment_date"=>$payment_date
];
}
return $amortization;
}