How to use XIRR from VBA Script - vba

Question

I have an Excel spreadsheet that shows deposits to a bank account, plus periodically I check the balance and put that in the spreadsheet. I'd like to make a macro that calculates the to-date equivalent return (i.e., if I have this sequence of deposits, and then the account balance is $X, then the equivalent rate of interest is Y%). For example, I might have:
1-Jan-2010 $100
22-Apr-2011 $200
14-Feb-2012 $310
28-Aug-2013 $500
9-May-2014 $790 # account lost value!
I can get the dates and deposits into a function (along with the ending balance) but I can't get XIRR to work right. I know this is ugly VBA (not a language I know) but here's what I have:
Public Function MyXIRR(Dates As Range, Trans As Range, Balance As Double)
Dim i As Integer
Dim x As Double
Dim dateArray() As Date
Dim valArray() As Double
ReDim dateArray(Dates.Count + 1)
ReDim valArray(Trans.Count + 1)
For i = 1 To Dates.Count
dateArray(i - 1) = Dates.Item(i)
Next i
For i = 1 To Trans.Count
valArray(i - 1) = Trans.Item(i)
Next i
dateArray(Dates.Count) = DateAdd("d", 1, Dates.Item(Dates.Count))
valArray(Trans.Count) = -1 * Balance
For i = 0 To Dates.Count
dateArray(i) = Format(dateArray(i), "dd/mm/yyyy")
Next i
MsgBox ("Hello")
x = Application.Xirr(valArray, dateArray, 0.01)
MsgBox (x)
' MyXIRR = Dates.Count * 100 + Trans.Count
' MyXIRR = dateArray(6)
MyXIRR = valArray(3)
End Function
(The comments and MsgBox at the end are my various attempts to figure out what's going on; ideally, I'd just have a formula in a cell: =MyXIRR( A2:A6, B2:B6, C6 ) which would return the equivalent interest rate.)
I think what's happening is that when I call Application.Xirr, I'm getting a #VALUE exception (error?) But I don't know how to debug it, examine the arrays passed to Xirr, or figure out what's wrong.

Answer 1

I don't know whether this is The Answer, or whether I've merely swept the problem under a different rug, but I was able to get my function to work reliably by converting the dateArray to an array of Strings, where each String is a parseable date.
Public Function MyXIRR(Dates As Range, Trans As Range, Balance As Double)
Dim i As Integer
Dim x As Double
Dim dateArray() As Date
Dim dateStrings() As String
Dim valArray() As Double
ReDim dateArray(Dates.Count)
ReDim valArray(Trans.Count)
ReDim dateStrings(Dates.Count)
For i = 1 To Dates.Count
dateArray(i - 1) = Dates.Item(i).Value
Next i
For i = 1 To Trans.Count
valArray(i - 1) = Trans.Item(i).Value
Next i
dateArray(Dates.Count) = DateAdd("d", 1, Dates.Item(Dates.Count))
valArray(Trans.Count) = -1 * Balance
For i = 0 To Dates.Count
dateStrings(i) = Format(dateArray(i), "mm/dd/yyyy")
Next i
MyXIRR = Application.WorksheetFunction.Xirr(valArray, dateStrings, 0.01)
End Function