Help with a small equation and loop

I need to calculate how much time it will take to pay off a credit card. I'll take any help.

Code:

#include <iostream>

using namespace std;



int main()


{

	 float bal,ir,payment,year, newbal,newbal2;


cout << "Enter credit card Balance" << endl;
cin >>bal;

cout <<"Enter Intrest rate" << endl;
cin >>ir;

cout << "Enter years:" << endl;
cin>> year;
for( newbal =1 ; newbal <=12 ; newbal++)
{

// Formula
payment = ((bal*ir)/year)+10; 

cout << " Payment each month:"<<  payment<< endl;



newbal = bal + ir - payment;



cout << newbal<<endl;
newbal2 = (newbal-(payment*12)+ir);
cout << newbal2<< endl;


cout <<"total amount months to pay of debt " <<newbal2<< endl;



	
}

system("pause");
	return 0;

Think about what controls your loop, and what calculates a new balance

> for( newbal =1 ; newbal <=12 ; newbal++)
> newbal = bal + ir - payment;
These are inconsistent.

Well, for starters. Your math is wrong.

Code:

newbal = bal + ir - payment;

Will not calculate the new balance properly.

Interest rate is a %. 6% of 100 is different that 6% of 1000.

So, divide you interest rate by one hundred.
Then the interest acquired is the balance times that interest rate divided by 100.

example:

5.98765% interest of 123456 dollars.
5.98765 / 100 = 0.0598765
123456 + (123456 * 0.0598765) = 130848.11


Also, you can if you chose to do this:

Code:

 newbal2 = (newbal-(payment*12)+ir);

Is fine, but you do NOT have to have a new variable every time you change something.
The following is just as valid:

Code:

 newbal = (newbal-(payment*12)+ir);

There are perfectly legit reasons to use the method you are using, I am just letting you know this incase you do not know.

Ok, now onto your program.
Play with the math on some paper and pencil and calculator. There is a simpler way of doing this than the method you are trying.

Alright, well I figured I need to change the loop, and x the percent by 100 so far. Still working on everything else.