Adding Integers In ListBox Using For Next?

I need to add integers in a listbox, using for next.
Dim intCount As Integer
Dim dblTotal As Double
' here are the lines of code that will perform the calculations
' to create a grand total.
For intCount = 1 To lstCosts.Items.Count
dblTotal += dblSubTotal += intCount
Next intCount
lblTotal.Text = dblTotal.ToString("C")

The amount of items in the list box is not seso I used the items.count. I have been getting the wrong result.
Private Sub btnCalculate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCalculate.Click
' Declarations.
Dim intCount As Integer
Dim dblTotal As Double
' here are the lines of code that will perform the calculations to create a grand total.
[Code] .....