Guys, Should I put the Function into the Forms and make it an "Private Sub"?

First of all does the Function work without errors?

What does your table structure look like?
What are the data types of the fields in the table?
Screenshots?

Hey Kelvin, I got an "Run-time Error '3075': Syntax Error (missing operator) in Query Expression 'EstimateID='.
The Contract Table's Fields: ContractID is an 'Autonumber' and Contract Version Number field is an 'Short Text Field'

Sorry, the VBA Code for the Estimate & Contract Version Number is the Same:

Function GenerateEstimateVersionNum() As String

    Dim curVersion As String
    Dim newVersion As String
    Dim maxVersion As Integer
    Dim Prefix As String
    Dim verCount As Long
  
    Prefix = "V"
    
    curVersion = DLookup("EstimateVersionNumber", "EstimateT", "EstimateID=" & EstimateID)

    If IsNull(curVersion) Then
        newVersion = "1"
    Else
        maxVersion = Nz(DMax("EstimateVersionNumber", "EstimateT", "EstimateID=" & EstimateID), 0)
        newVersion = Prefix & " " & CStr(Format(maxVersion + 1, "0.0"))
    End If

    GenerateEstimateVersionNum = newVersion

End Function

But the I tried to create another VBA Code for the Estimate & Contract Version Number which is:

Function GetNextEstimateVersionNum() As Long

    Dim strSQL As String
    Dim rs As Recordset
    Dim nextVersion As Long
      
    Dim tableName As String
    Dim versionFieldName As String
    
    tableName = "EstimateT"
    versionFieldName = "EstimateVersionNumber"
    
    strSQL = "SELECT MAX([" & versionFieldName & "]) AS MaxVersion FROM [" & tableName & "];"
    
    Set rs = CurrentDb.OpenRecordset(strSQL)
    
    If Not rs.EOF And Not rs.BOF Then
         nextVersion = rs("MaxVersion") + 1
    Else
         nextVersion = 1
    End If
    
    rs.Close
  
    GetNextEstimateVersionNum = nextVersion

End Function


Private Sub Form_BeforeUpdate(Cancel As Integer)

    Dim rs As Recordset
    Dim contractID As Long
    Dim currentVersion As Long
    Dim newVersion As Long
    
    Set rs = CurrentDb.OpenRecordset("ContractT")
    
    contractID = Me![ContractID]
    
    rs.FindFirst "[ContractID] = " & ContractID
    Do While Not rs.NoMatch
        currentVersion = rs![ContractVersionNumber]
        rs.FindNext "[ContractID] = " & ContractID
    Loop
    
    newVersion = currentVersion + 1
    
    rs.FindFirst "[ContractID] = " & ContractID
    
    rs.Edit
    rs![ContractVersionNumber] = newVersion
    rs.Update
    
    rs.Close
    Set rs = Nothing

End Sub

Hi James, I suggest you create two fields in your table -- an actual version number, and a version number for display purposes.  E.g.:

ActualVers   DisplayVers
5.1          Rev. 5.1.V
20.8         Rev. 20.1.V
2            Rev. 2.0.V

Then, all you need to do is just add 1 to the ActualVers field, which can be done with a simple update query.  Make DisplayVers a calculated field (="Rev. " & Format([ActualVers], "0.0") & ".V"), or you can update its value with VBA, so the display version is automatically generated.  That way you need very little VBA, or no VBA at all.

Okay Kelvin, sounds good. I will get right to it. Thanks for your help.

Hey Guys, I have figure out, here's the Code I have came up with:

Private Sub Form_BeforeUpdate(Cancel As Integer)
    
    Dim curVersion As String
    Dim nextVersion As String
    Dim maxVersion As String
    Dim prefix As String
    
    prefix = "V"
    
    curVersion = Nz(DLookup("EstimateActualVersionNumber", "EstimateT", "EstimateID=" & EstimateID), 0)
    
    If IsNull(curVersion) Then
        nextVersion = curVersion + 1
    Else
        maxVersion = Nz(DMax("EstimateActualVersionNumber", "EstimateT", "EstimateID=" & EstimateID), 0)
        nextVersion = prefix & " " & CStr(Format(maxVersion + 1, "0.0"))
        CurrentDb.Execute "UPDATE EstimateT SET EstimateActualVersionNumber=" & nextVersion & " WHERE EstimateID=" & Me.EstimateID
        MsgBox "Estimate Updated to Version " & nextVersion, vbInformation, "Estimate Version Updated"
    End If
      
    EstimateActualVersionNumber = nextVersion
    
End Sub

But I am getting an Error....

maxVersion is a string, so that's why maxVerson + 1 causes "type mismatch" error.  As I said earlier, you need a numeric field to store the version number, to make it easier to do such math calculations.

Kelvin, this is what you was talking about..

I got this VBA Code that work great, but I can't figure out how to get the Code to "Update the Version Number".

Function GenerateEstimateVerNum() As String

    Dim customNumber As String
    Dim lastNumber As String
    Dim Prefix As String
    Dim verCount As Long
    
    Prefix = "V"
    
    lastNumber = Nz(DMax("EstimateVersionNumber", "EstimateT"), 0)
    verCount = DCount("EstimateVersionNumber", "EstimateT")
    
    customNumber = Prefix & " " & Format(verCount + 1, "0.0")
    
    GenerateEstimateVerNum = customNumber

End Function

Hi James, you are still working with strings, which I've said you should avoid doing.  If version updates involve only adding 1 to the existing version, it should not take that much code, or even no code as I said.  Your last error "Invalid use of '.' ..." was also caused by "nextVersion" being a string, a non-numeric string at that.  In your second-last picture, "nextVersion" equals to "V1.0".  That was why "SET EstimateActualVersionNumber=" & nextVersion & ... caused an error, because you tried to assign a non-numeric string to a numeric field.  

Kevin you were Correct... I didn't see at first...

Here's the Final Code:

Private Sub Form_BeforeUpdate(Cancel As Integer)
      
    Dim newVersion As String
    Dim customNumber As String
    Dim lastNumber As String
    Dim Prefix As String
    Dim verCount As Long
    
    Prefix = "V"
  
    lastNumber = Nz(DMax("EstimateVersionNumber", "EstimateT", "EstimateID=" & EstimateID), 0)
    verCount = DCount("EstimateVersionNumber", "EstimateT", "EstimateID=" & EstimateID)
    customNumber = Prefix & " " & Format(verCount + 1, "0.0")
  
    EstimateVersionNumber = customNumber
    
End Sub