Thread: Mortgage calulator HW problem

Hello,

I am very new to programming and I have hit a stuck point in my code. This is for a mortgage calculator and we have to use the math.pow method. I am getting results, but the results are wrong. The monthly payment is coming out to big.

Here is what it should be:

Enter loan amount: 10000
Enter rate: 4.5
Enter number years: 3

The monthly payment is: $297.47


Here is what I'm getting.

Enter loan amount: 10000
Enter rate: 4.5
Enter number years: 3

The monthly payment is: $566.06

Here is my code. I believe my issue is in the math.pow formula. Can someone help my out?



Scanner in = new Scanner(System.in); // input object

double loanAmount; //user input
double interestRate; // user input
double yearNumber; // user input
double monthlyPayment; // answer to math
double finalPayment; // output
double monthNumber; // year number converted of months
double monthlyRate; // converted intersted rate


System.out.print("Enter loan amount: "); // Shows Line to input loan amount
loanAmount = Double.parseDouble (in.nextLine()); // gets input number


System.out.print("Enter rate: "); // Shows line to input rate amount
interestRate = Double.parseDouble (in.nextLine()); // gets input number

monthlyRate = interestRate * .01; //convert rate into decimal


System.out.print("Enter number years: "); //Shows line to input number of years
yearNumber = Double.parseDouble (in.nextLine()); // gets input number

monthNumber = yearNumber * 12; // total amount of months



monthlyPayment = Math.pow(1+ interestRate,monthNumber) / (Math.pow(1+interestRate, monthNumber)-1);


finalPayment = (loanAmount*monthlyRate*monthlyPayment); // gives the payment


System.out.printf("\nThe monthly payment is: $%.2f", monthlyPayment); // Shows monthly payment

I'm sorry. I don't understand how to use highlight tags. But the answer should be $297.47 in this example and I am getting $566.06. My answer is incorrect meaning the math must be wrong. I can't figure out where it is wrong.

--- Update ---

Here is the entire code.

package assignment2;

import java.util.Scanner;

/**
*
*
*/
public class Assignment2 {

/**
* @param args the command line arguments
*/
public static void main(String[] args) {
// TODO code application logic here

Scanner in = new Scanner(System.in); // input object

double loanAmount; //user input
double interestRate; // user input
double yearNumber; // user input
double monthlyPayment; // answer to math
double finalPayment; // output
double monthNumber; // year number converted of months
double monthlyRate; // converted intersted rate


System.out.print("Enter loan amount: "); // Shows Line to input loan amount
loanAmount = Double.parseDouble (in.nextLine()); // gets input number


System.out.print("Enter rate: "); // Shows line to input rate amount
interestRate = Double.parseDouble (in.nextLine()); // gets input number

monthlyRate = interestRate * .01; //convert rate into decimal


System.out.print("Enter number years: "); //Shows line to input number of years
yearNumber = Double.parseDouble (in.nextLine()); // gets input number

monthNumber = yearNumber * 12; // total amount of months



monthlyPayment = Math.pow(1+ interestRate,monthNumber) / (Math.pow(1+interestRate, monthNumber)-1);


finalPayment = (loanAmount*monthlyRate*monthlyPayment); // gives the payment


System.out.printf("\nThe monthly payment is: $%.2f", monthlyPayment); // Shows monthly payment
System.out.println();

}

}

convert your Annual interest rate into monthly interest rate. Your annual interest rate here is 4.5 which will become 4.5/100=0.045, 0.045/12=0.00375.

I convert the annual interest rate with
monthlyRate = interestRate * .01; //convert rate into decimal

Will that not do the same as /100?

4 Ways to Calculate Mortgage Payments - wikiHow

Do you have an example?

Originally Posted by Rods

4 Ways to Calculate Mortgage Payments - wikiHow

I read this before and it helped. I missed the part about monthly rate. so I just added this
yearRate = interestRate * .01; //convert rate into decimals
** monthlyRate = yearRate / 12; // convert rate to month rate

And now it works correctly. Thanks for your help everyone.

Excellent. Enjoy.