Listbox Value Not Registering for Calculation

Shouldn't LnTrmList.SelectedValue be LnTrmList.SelectedItem.Value?

I'm not in front of a box with VB on it, but I think that's where you're slightly awry.

Use your trace environment and watches to keep an eye on LnTrnList.SelectedItem.Value to check, or use a MsgBox to display the value...

MsgBox after the calculation showed that Months was registering as 0.

This is what I have:

        'The car price should appear in terms of dollars and cents.
        Dim carprice As Double
        'The APR needs two percentage points
        Dim interestrate As Double
        'Money down should be dollars and cents
        Dim moneydown As Double
        'Dim loan term As Double
        Dim loanterm As Double
        'Dim Payment as Double
        Dim payment As Double
        Dim monthlyinterest As Double
        Dim months As Double
        Dim loanamount As Double

        'Declare where the values are coming from
        carprice = Val(Carpricetext.Text)
        interestrate = Val(IRTextbox.Text)
        moneydown = Val(Dwnpymnttext.Text)
        loanterm = Val(LnTrmList.SelectedItem)

        loanamount = (carprice - moneydown)
        monthlyinterest = (interestrate / 100) / 12
        months = 12 * loanterm

        'calculate payments - rate * month = monthly payments
        payment = Pmt(monthlyinterest, months, -loanamount)

        'displays results
        paymenttxt.Text = payment
    End Sub

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And it still does not seem to do the calculation.  
It will not do the payment = line as "Argument 'NPer' is not a valid value."

What kind of values do you have in your ListBox?  I put in years, such as: 3, 4, 5 ,6 , 7, etc...

The values in the listbox are:
1
2
3
4
5

NPer is the number of months in the PMT calculation.

If your number of months is still showing as "0" then your calculation won't work.

I get the error "Argument 'NPer' is not a valid value." if I do this calculation:

Payment = Pmt(0.25, 0, 2000)

are you using SelectedItem or SelectedItem.value?  Does it make a difference?

After the changes, it worked perfectly for me.  =\

You could also make sure there is an item selected in the ListBox:

    If LnTrmList.SelectedIndex <> -1 Then
        loanterm = Val(LnTrmList.SelectedItem)

        loanamount = (carprice - moneydown)
        monthlyinterest = (interestrate / 100) / 12
        months = 12 * loanterm

        Debug.Print("loanterm = " & loanterm)
        Debug.Print("months = " & months)

        'calculate payments - rate * month = monthly payments
        payment = Pmt(monthlyinterest, months, -loanamount)

        'displays results
        paymenttxt.Text = payment        
    Else
        MessageBox.Show("Please select a Term!")
    End If

With the Debug.Prints() in there, what do you get in the Immediate window?

Predictably, I get: Please Select a Term.  I have no other code on this form.
This is all the code on this page:

Option Strict On

Public Class childform



    Private Sub calcbutton_Click(sender As System.Object, e As System.EventArgs) Handles calcbutton.Click
        'The car price should appear in terms of dollars and cents.
        Dim carprice As Double
        'The APR needs two percentage points
        Dim interestrate As Double
        'Money down should be dollars and cents
        Dim moneydown As Double
        'Dim loan term As Double
        Dim loanterm As Double
        'Dim Payment as Double
        Dim payment As Double
        Dim monthlyinterest As Double
        Dim months As Double
        Dim loanamount As Double

        'Declare where the values are coming from
        carprice = Val(Carpricetext.Text)
        interestrate = Val(IRTextbox.Text)
        moneydown = Val(Dwnpymnttext.Text)
        loanterm = CDbl(LnTrmList.SelectedItem)

        If LnTrmList.SelectedIndex <> -1 Then
            loanterm = Val(LnTrmList.SelectedItem)

            loanamount = (carprice - moneydown)
            monthlyinterest = (interestrate / 100) / 12
            months = 12 * loanterm

            Debug.Print("loanterm = " & loanterm)
            Debug.Print("months = " & months)

            'calculate payments - rate * month = monthly payments
            payment = Pmt(monthlyinterest, months, -loanamount)

            'displays results
            paymenttxt.Text = CStr(payment)
        Else
            MessageBox.Show("Please select a Term!")
        End If


     
    End Sub

End Class

I'm now in front of a VB machine as well.

I've recreated the problem quite simply (not bothered naming my textboxes etc).

And this works!

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim Payment As Double
        Dim loanamount As Double = (Val(TextBox1.Text) - Val(TextBox3.Text))
        Dim monthlyinterest As Double = (Val(TextBox2.Text) / 100) / 12
        Dim loanterm = Val(ListBox1.SelectedItem)
        Dim months = 12 * loanterm

        'calculate payments - rate * month = monthly payments
        Payment = Pmt(monthlyinterest, months, -loanamount)

        'displays results
        TextBox4.Text = Payment


    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        ListBox1.Items.Add("1")
        ListBox1.Items.Add("2")
        ListBox1.Items.Add("3")
        ListBox1.Items.Add("4")
        ListBox1.Items.Add("5")

    End Sub

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CSIP,

The only difference between your form and mine is that the listbox is shrunken to only show one value at a time with an arrow.

Wow, I hate to admit it, but my mistake with this was simply that I did not select the number (highlight).

Is your list box set to allow multiple selections?

If so, you need to read the selected values in a different way.

I'll set my box like that and see if it makes a difference.

Doh!

Glad you got to the bottom of it!

Fair split.  I'm happy :-)

Hehe!...did you by chance stay up all night?

Drink some coffee bud.   ;)