Need help with Math.pow Calculations

KenanCross · 02-12-2012, 09:38 PM

Hello again! Thanks for the help in the previous post I made last week. I'm in need of a little bit of assistance again.

I'm trying to get Math.pow to calculate and produce a result for my Mortgage Calculator project. I need to show a decreasing amount in the remaining balance of a mortgage loan. However the results I get seem to always stay the same. What am I doing wrong?

Code:

import java.text.DecimalFormat;
// This calculator will accurately calculate Mortgage Payments, while allowing for flexible variable adjustments 
//(i.e. Length of Payments, Principal, Interest.) Based on Service Request from McBride Financial

// Author: Kenan Cross //

public class MortgageCalculator {
    int i; // counter
    int termLimit = 30;
    int months;
    int payments; /* No. of monthly payments in mortgage*/
    int monthsPd = 12 * i; //Calculations of months paid so far
    double balPd; //Part of Balance Paid Formula
    double balPd2; //Part of Balance Paid Formula
    double balPd3; //Part of Balance Paid formula
    double balPdCalc; //Calculated result of balPd and balPd2
    double loanCalc;   //Power of Calculation for compound interest
    double powCalc; //Power of calculation variable
    double rate;
    double loanBalance;
    double loanInterest; //Calculated Loan with Interest
    double newLoanBalance; //Calculated Remaining Loan Balanace
    double annualRate;  //Computed Annual Rate
    double interestPlus; // rate + 1
    double interestPd;  // contains interest paid so far
    double interestAdj;
    double interestExp;
    int length; /* length of mortgage */
    double principle; /* Principle loan amount */
    double monthlyPayment; /* Calculated Monthly Payment */
    DecimalFormat dec;
    DecimalFormat percentage;


public static void main (String args[]){
	MortgageCalculator calc = new MortgageCalculator();
	calc.calculatePaymentAmount();
	calc.printPaymentAmount();
}

public MortgageCalculator(){
	months = 12;
	rate = 0.0575;
        principle = 200000;
	length = 30;
	dec = new DecimalFormat ("$0.00");
        percentage = new DecimalFormat("0.00%");
}

public void calculatePaymentAmount(){
	annualRate = ((rate)/(12));
        payments = (months) * (length);
	interestAdj = (annualRate)+(1);
        interestPlus = (rate + 1);
	interestExp = Math.pow(interestAdj, payments);
	monthlyPayment = principle * (annualRate * interestExp)/(interestExp - 1);
        loanCalc = principle * (Math.pow(interestAdj,(termLimit)));
}
//Above formula is based on M=P[i(1+i)^n]/[(1+i)^n-1] found on ifitbreaks.com/interest.htm//
public void printPaymentAmount (){
     System.out.println("Your Loan Amount is "+ dec.format(principle));
     System.out.println("Your Annual Rate is "+ percentage.format(rate));
     System.out.println("Your monthly payment amount is " + dec.format (monthlyPayment));
     System.out.println("Your principal balance with interest is " + dec.format (loanCalc));
    for (i=1; i <= termLimit; i++){
     //Loop set for the limit of Mortgage term
     powCalc = principle * (Math.pow(interestAdj, i))-1;
     balPd = monthlyPayment/annualRate;
     balPd2 = balPd - principle;
     balPd3 = 1 - Math.pow(annualRate, monthsPd);
     balPdCalc = balPd - (balPd2 * balPd3); 
     //formula is based on Amt Paid = (L/R - P)[(1+R)^X - 1] found
     // at http://www.infobarrel.com/Financial_Math:__Calculating_the_Mortgage_Balance_after_X_Number_of_Years
     interestPd = powCalc - principle;
     System.out.println("\tIn Year " + i + " you will have paid " + dec.format(interestPd) + " in interest.");
     System.out.println("\t Your remaining loan balance is " + dec.format(balPdCalc));
        try {
            Thread.sleep(5000);
            } 
        catch (InterruptedException e) {
            }
    }
 }
}

clinto · 02-15-2012, 06:18 PM

One thing that is happening is your monthsPd variable is being initialized at 12 * i; and never changes through each iteration. You want to move it into your for loop.

Code:

     for (i=1; i <= termLimit; i++){
     //Loop set for the limit of Mortgage term
     monthsPd = 12 * i;

Based on the formulas I see on http://www.infobarrel.com/Financial_...umber_of_Years I came up with this code:

Code:

    double amtPaid = (monthlyPayment/annualRate - principle) * (Math.pow(1 + annualRate, monthsPd) - 1);
    double mortgageBalance = loanCalc - amtPaid;

You would then print mortgageBalance.

Code:

System.out.println("\t Your remaining loan balance is " + dec.format(mortgageBalance));