Loan Program

[PDB1982]

I have to make a program that uses Periodic Payments and Unpaid Balance (When Payments are made). I am having trouble with the mathematics with my code (I know this isn't a math forum, but I think it's more of a coding issue). The formulas, and output are below.....do you see any issues with the math?

Periodic Payments:
R= (Li)/(1-(1+i)^(-mt)

i = (r/m) *** r is in decimal***

Unpaid Balance (UB in my functions)
UB = R * (1-(1+i)^-(mt-k))/i

Note that if payments are monthly, then m=12.

//Intro to Programming
//PAge 342-343, Assignment #9

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;

double periodic(double L, double r, double m, double t, double k, double i);
double unpaidbalance(double L, double r, double m, double t, double k, double i, double R);

int main()
{
	while (true)
	{
		double L, r, m, t, k, i, R, r2;

		cout << fixed << showpoint;
		cout << setprecision(2);

		cout << "Please Enter the Loan Amount : $ ";
		cin >> L;
		cout << "Please Enter the Interest Rate: ";
		cin >> r;
		cout << "Please Enter the Total Number of Payments: ";
		cin >> m;
		cout << "Please Enter the Length of the Loan (in Years): ";
		cin >> t;
		cout << "If You have made any month's payments, Enter the Number: ";
		cin >> k;
		cout << endl;

		r2 = r / 100;
		i = r2 / m;
		R = periodic(L,r,m,t,k,i);

		if (k>0)
		{
			cout << "Your Periodic Payment would be: $ " << periodic(L,r,m,t,k,i) << endl;
			cout << "Since You have made " << k << " payments, your remaining balance is: $"
				<< unpaidbalance(L,r,m,t,k,i,R) << endl;
			cout << "\n" << endl;
		}
		else
			cout << "Your Periodic Payment would be: $ " << periodic(L,r,m,t,k,i) << "\n";
			cout << endl;

	}
	cout << endl;
} // end of main

double periodic(double L, double r, double m, double t, double k, double i)
{
	double R, Y1, Y2, Y3;

	Y1 = L * i;
	Y2 = (1 + i);
	Y3 = (-1)*(m*t);
	R = Y1 / (1 - pow(Y2,Y3));

	return R;
}

double unpaidbalance(double L, double r, double m, double t, double k, double i, double R)
{
	double UB, Months, X1, X2;

	Months = 12;
	
	X1 = (1 + i);
	X2 = (-1) * ((Months * t) - k);
	UB = R * ((1 - pow(X1,X2)) / i);

	return UB;
}

This an example of my output:
Please Enter the Loan Amount : $ 1000
Please Enter the Interest Rate: 10.00
Please Enter the Total Number of Payments: 48
Please Enter the Length of the Loan (in Years): 4
If You have made any month's payments, Enter the Number: 12

Your Periodic Payment would be: $ 6.32
Since You have made 12.00 payments, your remaining balance is: $219.14

I think the Periodic Payment is coming out to high, which is making my unpaid balance funky. Any ideas?