Mortgage loan calculator - vb.net

Question

I need some help creating a mortgage loan calculator that allows the user to input the loan amount, loan years and loan rate and calculates the monthly mortgage payment and displays the amounts due for each month in a datagridview control. The problem is , i cannot seem to loop it using a for loop, i need to use the loop to display all the monthly payments but with my attempt it just repeats the same amounts for every month.Here is my code:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim loanAmount As Double
Dim loanYears As Integer
Dim loanRate As Double
Dim monthlyPayment As Double
Dim numberofPayments As Integer
Dim monthlyInterest As Double
Dim decimalInterest As Double
Dim interestPaid As Double
Dim newBalance As Double
Dim principle As Double
Dim n As Integer
Dim Pmt As Integer = 1
loanAmount = Val(TextBox1.Text)
loanYears = Val(TextBox2.Text)
loanRate = Val(TextBox3.Text)
decimalInterest = loanRate / 100
numberofPayments = loanYears * 12
monthlyInterest = decimalInterest / 12
Label1.Text = monthlyPayment
For Pmt = 1 To numberofPayments
n = n + 1
If n = numberofPayments + 1 Then
Exit For
End If
monthlyPayment = loanAmount * monthlyInterest / (1 - (1 + monthlyInterest) ^ -numberofPayments)
interestPaid = loanAmount * monthlyInterest
principle = monthlyPayment - interestPaid
newBalance = loanAmount - principle
Me.DataGridView1.Rows.Add(n, Math.Round(monthlyPayment, 2), Math.Round(interestPaid, 2), Math.Round(principle, 2), Math.Round(newBalance, 2))
Next
End Sub
If someone could please help me out , it would be much appreciated.
Thank you

Answer 1

You need loanAmount = loanAmount - principle inside the For, or some other statement that tracks the principle balance and uses it in each iteration. It looks like you're trying to do that with the newBalance variable, but each iteration status over with loanAmount, which never decreases, so the values never change. I would suggest tracing through your math and making sure that your algorithm is actually performing the operations you desire.