DateAdd function shows date from 1900 in VBA

Question

I have run to this weird problem and I really can't understand what is happening.

I have the code below

VBA Code:

Dim tddate As Date
Dim expdate As String
Dim inputdate As String

tddate = Worksheets("Sheet3").Range("pdate").Value
inputdate = TextBox1.Value
expdate = Format(DateAdd("m", 18, tddate), "dd/mm/yyyy")

If inputdate = expdate Then
Range("A1").Value = TextBox1.Value
Else
MsgBox "Input the correct date"
Cancel = True
End If

It compares the user input with the date that MUST be in a textbox...Until yesterday it worked PERFECT with no problems at all

Today that I continued my work on the excel project If I Debug.Print the expdate varieable the date that it shows is 30/06/1901 !!!!!!

PS. If I Debug.Print Now it shows the correct date PS.2. I am using Excel 2019 but I tried the workbook on a different laptop with Excel 2016 and shows the same thing. (The second try is because I changed my RAM yesterday -every time in my system is correct - and thought I messed up something)

Answer 1

Try working with true date values, not text:

Dim tddate      As Date
Dim expdate     As Date
Dim inputdate   As Date

tddate = Worksheets("Sheet3").Range("pdate").Value
If IsDate(TextBox1.Value) Then
    inputdate = DateValue(TextBox1.Value)
    expdate = DateAdd("m", 18, tddate)
    If DateDiff("d", inputdate, expdate) = 0 Then
        Range("A1").Value = inputdate
    Else
        Cancel = True
    End If
Else
    Cancel = True
End If

If Cancel Then
    MsgBox "Input the correct date"
End If