faiz programı visual studio

Public Class Form1
Dim pv, pmt, rate, nper As Double
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
nper = (TextBox2.Text)
If TextBox1.Text > 1 Then rate = TextBox1.Text / 100
Pmt = TextBox3.Text
PV = TextBox4.Text

Label6.Text = -(Financial.FV(rate / 12, nper, pmt, pv, DueDate.BegOfPeriod))


End Sub
End Class