Error: System.ArgumentOutOfRangeException: 'Year, Month, and Day parameters describe an un-representable DateTime.'

Can someone help me?

My algorithm should be this:
(Note: I used DateEdit from DevExpress not DateTimePicker)

This is my output
OBTAForTheMonthDateEdit - DateEdit1
OBTADeadlineDateEdit - DateEdit2 (disable for display use only)
LiquidationDeadlineDateEdit - DateEdit3 (disable for display use only)

Example: OBTAForTheMonthDateEdit the selected date is = 12/1/2022 (you can choose any day it doesn't matter)
Display: OBTADeadlineDateEdit = 11/18/2022 (should be the 18th day of the month and before the month you chose.)
LiquidationDeadlineDateEdit = 1/5/2023 (should be the 5th day of the month and after the month you chose.)

I used this code but error: System.ArgumentOutOfRangeException: 'Year, Month, and Day parameters describe an un-representable DateTime.'

    Private Sub OBTAForTheMonthDateEdit_TextChanged(sender As Object, e As EventArgs) Handles OBTAForTheMonthDateEdit.TextChanged
       Dim dt As Date = OBTAForTheMonthDateEdit.EditValue

       OBTADeadlineDateEdit.Text = New DateTime(dt.Year, dt.Month - 1, 18)
       LiquidationDeadlineDateEdit.Text = New DateTime(dt.Year, dt.Month + 1, 5)
    End Sub

Please help me regarding for this matter. thank you so much!

> Example: OBTAForTheMonthDateEdit the selected date is = 12/1/2022

If that's true then what do you think the value of dt.Month - 1 will be? It will be zero. Is zero a valid month? No it is not, so that's your problem. Rather than adding or subtracting from the month value and then constructing a date, you should be constructing the date first, then adding or subtracting a month:

OBTADeadlineDateEdit.Text = New DateTime(dt.Year, dt.Month, 18).AddMonths(-1)
LiquidationDeadlineDateEdit.Text = New DateTime(dt.Year, dt.Month, 5).AddMonths(1)

EDIT:

I realised that the specified input was in US format, in which case it represents December 1st rather than January 12th. The issue is still basically the same though. It just means that the specific issue is the addition producing 13 rather than the subtraction producing zero. The solution is still the same, i.e. construct the Date value first, then add or subtract a month. I tested my solution like this:

Dim dt = #12/1/2022#
Dim dt1 = New Date(dt.Year, dt.Month, 18).AddMonths(-1)
Dim dt2 = New Date(dt.Year, dt.Month, 5).AddMonths(1)

Console.WriteLine(dt1.ToLongDateString())
Console.WriteLine(dt2.ToLongDateString())

and the output was:
<pre>
Friday, 18 November 2022
Thursday, 5 January 2023
</pre>
exactly as you'd expect.