Excel PMT function in JS

Question

I found i little snipet on internet, about PMT calculate.

function PMT(i, n, p) {
 return i * p * Math.pow((1 + i), n) / (1 - Math.pow((1 + i), n));
}
function C         


        

Answer 1

NaN means "Not A Number".

Make sure you check for each input value whether it is numeric. Throw an error message if one is not, or set it to 0, depending on whether it's essential to your calculation or not.

A good collection of the best ways to check a value for whether it's numeric is this SO question: Validate numbers in JavaScript - IsNumeric()

Answer 2

This question's been dead for over a year, but I recently needed to do the same thing. Here's what I came up with:

function pmt(rate_per_period, number_of_payments, present_value, future_value, type){
    if(rate_per_period != 0.0){
        // Interest rate exists
        var q = Math.pow(1 + rate_per_period, number_of_payments);
        return -(rate_per_period * (future_value + (q * present_value))) / ((-1 + q) * (1 + rate_per_period * (type)));

    } else if(number_of_payments != 0.0){
        // No interest rate, but number of payments exists
        return -(future_value + present_value) / number_of_payments;
    }

    return 0;
}

type needs to be 1 or 0, same as Excel's. The rate_per_period needs to be a decimal (eg: 0.25, not 25%).

An example:

/* Example: */
var interest    = 0.07,     // Annual interest
    years       = 5,        // Lifetime of loan (in years)
    present     = 10000,    // Present value of loan
    future      = 20000,    // Future value of loan
    beginning   = 1;        // Calculated at start of each period

var payment = -pmt(interest / 12,   // Annual interest into months
                   years * 12,      // Total months for life of loan
                   present,
                   future,
                   beginning);

And the payment for the example period (month) is ~$474.60.

Note the negation of the result, as the amount is a dedection - ie: costs you $474 - the result is a negative value. Were the result to be a credit, the result would be a positive. Generally you'll want to keep it as a negative/positive, but if you were displaying it in a format like Total Debt: $XYZ, you'd want to convert it to a positive.

Answer 3

Try it like this:-

function CalculatePMTFromForm(idLoanAmount, idAnnualInterestRate, idMonths, idResult) {
 var i = parseFloat($('#' + idAnnualInterestRate).val()) / 1200;
 var n = parseFloat($('#' + idMonths).val());
 var p = parseFloat($('#' + idLoanAmount).val());
 var pmt = PMT(i, n, -p);
 $('#' + idResult).val(pmt.toFixed(2));
}

The .val() is likely returning a string type not a number type.