[SOLVED] Monthly Payments Calculator

[gamerzfuse]

I know there are many calculators out there that calculate monthly payments, etc.. but I just need a simple one that calculates (in a table) the Monthly payments for a vehicle over certain months at different money down at a set interest amount.

 

Example:

 

If I knew where to start that would be super helpful. I am more than willing to build it myself, but I don't even understand the payments myself (not the best Accountant here)

 

Any ideas?

[Ken2k7]

Well, start with the formula to calculate those numbers. Have you gotten that far?

[gamerzfuse]

I'm still trying to figure that out.

I'm going to go into the dealership and just see if I can get someone else to do the formulas for me.

My headache is too much already.

Then I guess I can just manually calculate each one?

[gamerzfuse]

I got it authorized by them to skip that and just program a calculator.

Is it easiest to code a calculator in PHP or in Javascript or what?

I just need a simple one with Months, Interest Rate, Downpayment, etc.

 

 

[xtopolis]

Depends on how accurate the calculations need to be.

 

Javascript would be convenient and relatively easy, should the calculations be ok if they are pretty close.

 

PHP with the BC math extension would give more exacting results, and you could use Ajax to make it more user friendly (read: no page refreshing).

 

You only need to figure out the formula, PHP can do the rest.  Javascript can handle a lot as well.

[gamerzfuse]

I would love to use PHP as I am quickly becoming much better at it and the possibilities of PHP are endless from what I have seen.

I'm looking into these math functions and they should work.

 

I'll probably have a couple <input> fields that need to be multiplied, shouldn't require anything but multiplication.. although the actual Amortization formula is much more complex and requires ^ (to the power of) values also.

 

I imagine I will easily find the answer while googling in the morning, but I assume there is a way to set input forms to $variables without much hassle?

 

Thanks for all your help, this is the best learning experience I've had in coding since I read HTML For Dummies front to back

[xtopolis]

It is really easy..  If you use ajax, technically you don't have to really worry about the form because you'll never actually submit it... (you take the values and append them to the url string).

[Ken2k7]

man pow

 

^ that function will become useful if you don't know it already. I love the name of that function. POW!!! Say it with pride!

[gamerzfuse]

Got it. Thanks!

Looking into all this soon.

Never used Ajax before, but if you can enlighten me I would be very excited to learn!

[Ken2k7]

Depends on what would enlighten you?

[gamerzfuse]

Well.. I'm going to start Googling Ajax calculator and such.

If I can find a generator that saves me time, I will generate a calculator and then clone it so I know how it all works.

[ionik]

Here is a payment calculator I wrote for car payments ...... you need to input the amounts in PHP but it works great

 

<?php

/*
* Fixed Rate Interest Loan Calulator
*/

// Do you pay on the amount at time of loan purchase?
// Or do you pay on the amount of the that you currently owe?
// Options
// ---------------------
// amountOwed | timeofPur
$loanType = 'amountOwed';

//Interest Rate
//  1-.00
$rate = '.23';
$rateYr = $rate / 365.5;
// Amount Of Loan
$amount = 10750;

// Pay Cycle In Days
$payLength = 14;

$paymentAmounts = 176;

$currentDay = 0;
$totalDays = 0;
$totalInterest = 0;
$totalInterestPayments = array();
$totalAmountPaid = 0;
$totalAmountOwed = $amount;
$lastPayment = 0;
$totalPayments = 0;
echo '<span style="font-size: 10px;">';
// Start calulating the total length
while ($totalAmountOwed > 0)
{
    // Are we adding interest?
    if ($currentDay == 365) {
        // Add in loan interest
        $interestAdd = ($loanType == 'amountOwed') ? $rate * $totalAmountOwed : $rate * $amount;
        $totalAmountOwed += $interestAdd;
        $totalInterest += $interestAdd;
        $currentDay = 0;
echo ' ------------------------------- <br /><br /> INTEREST ADDING <br /><br />';
echo '<strong>Added Interest : </strong> $'.round($interestAdd, 2).' Loan Balance is now $'.round( $totalAmountOwed, 2).' <br /><br />';
echo '<br /><br /> ------------------------------- <br /><br />';
    } else {
        $currentDay++;
    }
    
    if ($lastPayment == $payLength)
    {
if ($totalAmountOwed < $paymentAmounts)
        {
	$finalPaymentAmount = $totalAmountOwed;
                $paymentAmounts = $totalAmountOwed;
}
        // Get the total amount we are paying in interest add to array
        $interestPaid = $payLength * $rateYr * $totalAmountOwed;
        $totalPayments++;
        $totalInterestPayments[] = $interestPaid;
        $totalAmountPaid += $paymentAmounts;
        $totalAmountOwed = $totalAmountOwed - $paymentAmounts;
        $lastPayment = 0;
if ($finalPaymentAmount)
{
	echo '<strong>Making final payment of $'.round($paymentAmounts, 2).' and $'.round($interestPaid, 2).' of it is interest <br /><br /> ------------------------------- <br /><br /> LOAN IS PAID IN FULL <br /><br /> ------------------------------- <br /><br />';
}
else
{
	echo '<strong>Making a payment of $'.round($paymentAmounts, 2).' and $'.round($interestPaid, 2).' of it is interest loan balance is now $'.round($totalAmountOwed, 2).' <br /><br />';
}
    }
    else
    {
        $lastPayment++;
    }
    
    $totalDays++;
}

$interestAddedCount = count($totalInterestPayments);
foreach ($totalInterestPayments as $k => $v)
{
    $a++;
    $interestTotal += $v;
}
$interestToward = $interestTotal / $interestAddedCount;

$yearDay = 0;
$year = 0;
$monthCount = 0;
while( $totalDays != 0)
{
    if ($yearDay == 365) {
        $year++;
        $yearDay = 0;
    } else {
        $yearDay++;
    }

    if ($totalDays < 365) {
        if ($dayMonth != 30) {
            $dayMonth++;
        } else {
            $monthCount++;
            $dayMonth = 0;
        }
    }
    
    $totalDays--;
}

$interestPercentage = round(($interestToward / $paymentAmounts) * 100);

// Breakdown some stats!
echo 'Total Payments : '.$totalPayments.' <br />';
echo 'Final Payment Amount : $'.round($finalPaymentAmount,2).' <br />';
echo 'Loan Length : '.$year.' Year(s) '.$monthCount.' Month(s) '.$dayMonth.' Day(s) <br />';
echo 'Interest Paid : $'.round($totalInterest, 2).' <br />';
echo 'Total Cost of Loan : $'.round($totalInterest + $amount, 2).' <br />';
echo 'On Average You will be paying : $'.round($interestToward, 2).' towards interest each payment or '.$interestPercentage.'% of each payment is interest';
?>
</span>

[gamerzfuse]

Here is a payment calculator I wrote for car payments ...... you need to input the amounts in PHP but it works great

 

Wow.. thanks mate!

That's alot more than I expected in an answer.