calculate Income Tax using vb.net

Private Sub btnCalc_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCalc.Click
        'declare variables and constants
        Const conLanctax As Double = 0.01
        Const conFica As Double = 0.062
        Const conMedi As Double = 0.0125
        Const conpatax As Double = 0.0307
        Dim decnetpay As Decimal
        Dim decOver As Decimal
        Dim decweek1 As Decimal
        Dim decweek2 As Decimal
        Dim decrate As Decimal
        Dim declanctax As Decimal
        Dim decpatax As Decimal
        Dim decfica As Decimal
        Dim decmedi As Decimal
        Dim decfed As Decimal
        Dim decotrate As Decimal
        Dim decotpay As Decimal
        Dim decgross As Decimal
        Dim decover2 As Decimal
        Dim decotpay2 As Decimal
        Dim decbenefits As Decimal
        Dim decpay As Decimal
        Dim strStatus As String

        'determine if the information entered is numeric
        If IsNumeric(txtweek1.Text) Then
            decweek1 = Val(txtweek1.Text)
        Else
            MsgBox("Please enter a number in the box", MsgBoxStyle.Critical, "Number Required")
        End If
        If IsNumeric(txtweek2.Text) Then
            decweek2 = Val(txtweek2.Text)
        Else
            MsgBox("Please enter a number in the box", MsgBoxStyle.Critical, "Number Required")
        End If
        If IsNumeric(txtRate.Text) Then
            decrate = Val(txtRate.Text)
        Else
            MsgBox("Please enter a number in the box", MsgBoxStyle.Critical, "Number required")
        End If
        If IsNumeric(txtbenefits.Text) Then
            decbenefits = Val(txtbenefits.Text)
        Else
            MsgBox("Please enter a number in the box", MsgBoxStyle.Critical, "Number Required")
        End If

        'determine if overtime will be calculated
        If decweek1 > 40 Then
            decOver = decweek1 - 40
            decotrate = decrate * 1.5
            decotpay = decOver * decotrate
        End If
        If decweek2 > 40 Then
            decover2 = decweek2 - 40
            decotrate = decrate * 1.5
            decotpay2 = decOver * decotrate
        End If
        'Calculate the gross pay and determine taxes
        decpay = (decrate * ((decweek1 - decOver) + (decweek2 - decover2))) + (decotpay + decotpay2)
        decgross = decpay - decbenefits
        lblgross.Text = FormatCurrency(decpay, 2)
        declanctax = decgross * conLanctax
        lblLanc.Text = FormatCurrency(declanctax, 2)
        decpatax = decgross * conpatax
        lblPA.Text = FormatCurrency(decpatax, 2)
        decfica = decgross * conFica
        lblFica.Text = FormatCurrency(decfica, 2)
        decmedi = decgross * conMedi
        lblMedi.Text = FormatCurrency(decmedi, 2)
        strStatus = cboStatus.Text
        Select Case strStatus
            Case Is = "Single"
                Select Case decgross
                    Case Is < 290.38
                        decfed = decgross * 0.1
                    Case Is < 1178.84
                        decfed = ((decgross - 290.38) * 0.15) + 29.04
                    Case Is < 2853.84
                        decfed = ((decgross - 1178.84) * 0.25) + 162.3
                    Case Is < 5953.68
                        decfed = ((decgross - 2853.84) * 0.28) + 581.06
                    Case Is < 12944.23
                        decfed = ((decgross - 5953.68) * 0.33) + 1437.14
                    Case Is > 12944.23
                        decfed = ((decgross - 12942.3) * 0.35) + 3755.88
                End Select
            Case Is = "Married"
                Select Case decgross
                    Case Is < 580.76
                        decfed = decgross * 0.1
                    Case Is < 2357.69
                        decfed = ((decgross - 580.76) * 0.15) + 58.08
                    Case Is < 4757.69
                        decfed = ((decgross - 2357.69) * 0.25) + 324.62
                    Case Is < 7248.08
                        decfed = ((decgross - 4757.69) * 0.28) + 924.62
                    Case Is < 12944.23
                        decfed = ((decgross - 7248.08) * 0.33) + 1621.92
                    Case Is > 12944.23
                        decfed = ((decgross - 12944.23) * 0.35) + 3501.65
                End Select
            Case Is = "Seperated"
                Select Case decgross
                    Case Is < 290.38
                        decfed = decgross * 0.1
                    Case Is < 1178.84
                        decfed = ((decgross - 290.38) * 0.15) + 29.04
                    Case Is < 2378.85
                        decfed = ((decgross - 1178.84) * 0.25) + 162.3
                    Case Is < 3624.04
                        decfed = ((decgross - 2378.85) * 0.28) + 462.31
                    Case Is < 6472.12
                        decfed = ((decgross - 3624.04) * 0.33) + 810.96
                    Case Is > 6472.12
                        decfed = ((decgross - 6472.12) * 0.35) + 1750.83
                End Select
            Case Is = "Head of Household"
                Select Case decgross
                    Case Is < 413.46
                        decfed = decgross * 0.1
                    Case Is < 1578.85
                        decfed = ((decgross - 413.46) * 0.15) + 41.35
                    Case Is < 4076.92
                        decfed = ((decgross - 1578.85) * 0.25) + 216.15
                    Case Is < 6601.92
                        decfed = ((decgross - 4076.92) * 0.28) + 840.67
                    Case Is < 12944.23
                        decfed = ((decgross - 6601.92) * 0.33) + 1547.67
                    Case Is > 12944.23
                        decfed = ((decgross - 12944.23) * 0.35) + 3640.63
                End Select
        End Select
        decnetpay = decgross - declanctax - decpatax - decfica - decmedi - decfed
        lblFed.Text = FormatCurrency(decfed, 2)
        lblPay.Text = FormatCurrency(decnetpay, 2)
    End Sub