I am using the NPV() function in VB.NET to get NPV for a set of cash flows.

However, the result of NPV() is not consistent with my results performing the calculation manually (nor the Investopedia NPV calc... which matches my manual results)

My correct manual results and the NPV() results are close, within 5%.. but not the same...

Manually, using the NPV formula: NPV = C0 + C1/(1+r)^1 + C2/(1+r)^2 + C3/(1+r)^3 + .... + Cn/(1+r)^n

The manual result is stored in RunningTotal With rate r = 0.04 and period n = 10

Here is my relevant code:

EDIT: Do I have OBOB somewhere?

    YearCashOutFlow = CDbl(TxtAnnualCashOut.Text)
    YearCashInFlow = CDbl(TxtTotalCostSave.Text)

    YearCount = 1

    PAmount = -1 * (CDbl(TxtPartsCost.Text) + CDbl(TxtInstallCost.Text))
    RunningTotal = PAmount
    YearNPValue = PAmount
    AnnualRateIncrease = CDbl(TxtUtilRateInc.Text)

    While AnnualRateIncrease > 1
        AnnualRateIncrease = AnnualRateIncrease / 100
    End While
    AnnualRateIncrease = 1 + AnnualRateIncrease

    ' ZERO YEAR ENTRIES
    ListBoxNPV.Items.Add(Format(PAmount, "currency"))
    ListBoxCostSave.Items.Add("$0.00")
    ListBoxIRR.Items.Add("-100")
    ListBoxNPVCum.Items.Add(Format(PAmount, "currency"))
    CashFlows(0) = PAmount
    ''''

    Do While YearCount <= CInt(TxtLifeOfProject.Text)
        ReDim Preserve CashFlows(YearCount)

        CashFlows(YearCount) = Math.Round(YearCashInFlow - YearCashOutFlow, 2)
        If CashFlows(YearCount) > 0 Then OnePos = True


        YearNPValue = CashFlows(YearCount) / (1 + DiscountRate) ^ YearCount
        RunningTotal = RunningTotal + YearNPValue

        ListBoxNPVCum.Items.Add(Format(Math.Round(RunningTotal, 2), "currency"))
        ListBoxCostSave.Items.Add(Format(YearCashInFlow, "currency"))

        If OnePos Then
            ListBoxIRR.Items.Add((IRR(CashFlows, 0.1)).ToString)
            ListBoxNPV.Items.Add(Format(NPV(DiscountRate, CashFlows), "currency"))
        Else
            ListBoxIRR.Items.Add("-100")
            ListBoxNPV.Items.Add(Format(RunningTotal, "currency"))
        End If

        YearCount = YearCount + 1
        YearCashInFlow = AnnualRateIncrease * YearCashInFlow
    Loop