Mega Code Archive
A suite of financial management functions including present and future
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value of an annuity and a loan payment calculation function
<?php
/*
VARIABLES:
$m = number of periods per year. For instance, if you are For
instance, if you are making payments monthly then this number is 12.
$n = total number of periods. For instance, if you are
compounding monthly for 5 years, this number would be 60 (12 months
x 5 years).
$R = annual interest rate (represented as a decimal, 8% = .08)
$pmt = first or re-occuring payment or receipt (this number cannot
vary for differing cash flows)
$principal = present value of an annuity, or current principal of a
loan used in the PaymentCalc function
*/
// present value of an Annuity
// uses include defining Remaining Principal of a loan/mortgage
function PVannuity ($m,$n,$R,$pmt) {
$Z = 1 / (1 + ($R/$m));
return ($pmt * $Z * (1 - pow($Z,$n)))/(1 - $Z);
}
// Given the compounding, principal, interest rate, you can calculate
the monthly payment
function PaymentCalc ($m,$n,$R,$principal) {
$Z = 1 / (1 + ($R/$m));
return ((1 - $Z) * $principal) / ($Z * (1 - pow($Z,$n)));
}
// future value of an Annuity
function FVannuity ($m,$n,$R,$pmt) {
return $pmt * ((pow((1 + $R/$n),$m) - 1)/($R/$n));
}
// present value of a single payment
function PVsingle ($m,$n,$R,$pmt) {
return $pmt * pow((1 + $R/$m),-$n);
}
// future value of a single payment
function FVsingle ($m,$n,$R,$pmt) {
return $pmt * pow((1 + $R/$m),$n);
}
// future value of a single payment with continuous compounding
function FVperp ($m,$n,$R,$pmt) {
return $pmt * exp($R * ($n/$m));
}
?>
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