Hospital Charges form

[Kyonn]

Trying to figure out why exactly it will display the total value of decMiscCharges + decCharges. Any advice would be appreciated.

Option Strict On
Option Explicit On
Public Class Form1
 
    Private Sub btnCalculate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCalculateCharges.Click
 
        'declare all variables
        Dim decCharge As Decimal
        Dim intLengthOfStay As Integer
        Dim decMedCharges As Decimal
        Dim decSurgicalCharge As Decimal
        Dim decDayRate As Decimal
        Dim decMiscCharge As Decimal
        Dim decSurgicalCharges As Decimal
        Dim decTotalCharge As Decimal
        Dim decMeds As Decimal
        Dim decLabFee As Decimal
 
        If isValid(decMeds, decSurgicalCharge, intLengthOfStay, decLabFee) = True Then
            decCharge = CalcStayCharge(intLengthOfStay, decDayRate)
            decMiscCharge = CalcMiscCharges(decMedCharges, decSurgicalCharges, decLabFee)
            decTotalCharge = CalcTotalCharge(decMiscCharge, decCharge)
            txtTotalCost.Text = decTotalCharge.ToString("c2")
        End If
 
    End Sub
 
    Private Function isValid(ByRef decMeds As Decimal, ByRef decSurgeicalCharge As Decimal, _
                            ByRef intLengthOfStay As Integer, ByRef decLabFee As Decimal) As Boolean
 
        Return isValidStay(intLengthOfStay) AndAlso isValidMedication(decMeds) _
        AndAlso isValidSurgical(decSurgeicalCharge) AndAlso CBool(isValidLabFee(decLabFee))
 
        Return isValid
    End Function
 
    Private Function isValidStay(ByRef intLengthOfStay As Integer) As Boolean
        'Declare Boolean
        Dim isGood As Boolean
        'Declare Constants
        Const c_DaysError As String = "Length of stay must be a whole number between 0 and 100"
        Try
            intLengthOfStay = Convert.ToInt32(txtLengthOfDays.Text)
            If intLengthOfStay >= 0 And intLengthOfStay <= 100 Then
                isGood = True
            Else
                isGood = False
            End If
        Catch ex As Exception
            isGood = False
        End Try
        If isGood = False Then
            MessageBox.Show(c_DaysError)
            txtLengthOfDays.SelectAll()
            txtLengthOfDays.Focus()
        End If
        Return isGood
    End Function
 
    Public Function isValidLabFee(ByVal decLabFee As Decimal) As Decimal
 
        'Declare Variable
        Dim isGood As Boolean
        'Declare Constant
        Const c_LabFeeError As String = "Medication must be between 0 and 10,000"
 
        Try
            decLabFee = Convert.ToDecimal(txtLabFees.Text)
            If decLabFee >= 0D And decLabFee <= 10000D Then
                isGood = True
            Else
                isGood = False
            End If
        Catch ex As Exception
            isGood = False
            MessageBox.Show(c_LabFeeError)
            txtLabFees.SelectAll()
            txtLabFees.Focus()
        End Try
        Return CDec(isGood)
    End Function
 
    Public Function isValidMedication(ByVal decMedCharges As Decimal) As Boolean
 
        'Declare Variable
        Dim isGood As Boolean
        'Declare Constant
        Const c_MedicationError As String = "Medication must be between 0 and 10,000"
 
        Try
            decMedCharges = Convert.ToDecimal(txtMedicationCharges.Text)
            If decMedCharges >= 0D And decMedCharges <= 10000D Then
                isGood = True
            Else
                isGood = False
            End If
        Catch ex As Exception
            isGood = False
            MessageBox.Show(c_MedicationError)
            txtMedicationCharges.SelectAll()
            txtMedicationCharges.Focus()
        End Try
        Return isGood
    End Function
 
    Public Function isValidSurgical(ByVal decSurgicalCharges As Decimal) _
    As Boolean
 
        'Declare Variables
        Dim isGood As Boolean
        'Declare constants
        Const c_SurgicalError As String = "Surgical must be between 0 and 500,000"
 
        Try
            decSurgicalCharges = Convert.ToDecimal(txtSurgicalCharges.Text)
            If decSurgicalCharges >= 0D And decSurgicalCharges <= 500000D Then
                isGood = True
            Else
                isGood = False
            End If
        Catch ex As Exception
            isGood = False
            MessageBox.Show(c_SurgicalError)
            txtSurgicalCharges.SelectAll()
            txtSurgicalCharges.Focus()
        End Try
        Return isGood
    End Function
 
    Private Sub txtLabFees_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtLabFees.TextChanged
 
    End Sub
End Class
 
Module modTotalCharge
    Public Function CalcTotalCharge(ByRef decMiscCharge As Decimal, ByRef decCharge As Decimal) _
    As Decimal
        Return decMiscCharge + decCharge
    End Function
End Module
 
Module modMiscCharge
    Function CalcMiscCharges(ByRef decMedCharges As Decimal, ByRef decSurgicalCharges As Decimal, ByRef decLabFee As Decimal) _
    As Decimal
        Return decMedCharges + decSurgicalCharges + decLabFee
    End Function
End Module
 
Module modStayCharge
    Public Function CalcStayCharge(ByVal intLengthofStay As Integer, ByVal decDayRate As Decimal) _
    As Decimal
        decDayRate = 350D
        Return intLengthofStay * decDayRate
    End Function
End Module