Question

am only getting the interest amount an not the amount i suppose to pay a month can you please tell me where am going wrong thanks.

import java.util.Scanner;

/**
 *
 * @author 
 */
public static void main(String[] args) {
       Scanner input = new Scanner(System.in);
       //variabled decleared
       double rate;
       double payment;
       //input
       System.out.print("Enter Loan Amount:");
       double principal = input.nextDouble();
       System.out.print("Enter Annual Interest:");
       double interest = input.nextDouble();
       System.out.print("Total payment type:");
       String period = input.next();
       System.out.print("Enter Loan Length :");
       int length = input.nextInt();

       //proces
       rate = interest / 100;

       if (period.equals("monthly")) {
           double n = length * 12;
           payment = principal * (rate * Math.pow((1 + rate), n) / Math.pow((1 + rate), n));
          System.out.printf("Your Monthly Sum is %.2f",payment);
       }
}

Answer 1

Your error is here:

principal * rate * Math.pow((1 + rate), n) / Math.pow((1 + rate), n)

This is the same as having only principal * rate. You are saying x = b * a / a.
Replace to:

 payment = principal * Math.pow((1 + rate), n);

n is the number of years, you can not do n = length / 12 to get Monthly. You should do instead:

payment = (principal * Math.pow((1 + rate), n)) / 12;