Java: How do I display how many months it took?

Heres my code:

import java.util.*;

public class LoanCalculator {

  static Scanner console = new Scanner(System.in);

  public static void main(String[] args) {

    //Declare variables
    double loanAmount;
    double interestRate;
    double monthlyPayment;
    double interest = 0;
    double principal = 0;
    int months;

    System.out.print("Enter the amount of your loan: ");
    loanAmount = console.nextDouble();
    System.out.println();

    System.out.print("Enter the interest rate per year: ");
    interestRate = console.nextDouble();
    System.out.println();

    System.out.print("Enter your monthly payment amount: ");
    monthlyPayment = console.nextDouble();
    System.out.println();

    interestRate = (interestRate / 12) /100;

    for (months = 1; months <= loanAmount; months++)
    {
        interest = (loanAmount * interestRate);
        principal = monthlyPayment - interest;
        loanAmount = loanAmount - principal;
        System.out.println(months);
    }
  }
}

I want the program to output how many months the loan took to pay off, but it's listing every month. How can I do this? Also if the monthly payment is less then the first month's interest then the loan amount will increase, how can I warn the user if this happens?