Edited Version: Very Urgent Date Calculation

Hi, How can i calculate the date out? i am using vb sql server database...db saved my date as dd/MM/yyyy, form display my date as dd/MM/yyyy too

1.I have a selected date by user from calendar in tb_dop.text 

2.creditDate.text for user to enter number of days to add to tb_dop.text date

3.dDate.text to display the calculated date Private Sub Calendar1_SelectionChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Calendar1.SelectionChanged

'display selected date from calendar

tb_dop.Text = Calendar1.SelectedDate()

End SubPrivate Sub btn_add2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_add2.ClickDim myDate As New DateTime

myDate = tb_dop.Text

Dim i As Integer

i = creditDate.TextDim dDate As New DateTime

dDate = myDate.AddDays(i)

dueDate.Text = dDate

ERROR
The conversion of char data type to smalldatetime data type resulted in an out-of-range smalldatetime value.
The statement has been terminated.

I know it is becos diff format of date calculation, there4, how can i change it to calculate in mm/dd/yyyy format? Funny rite? i can saved and display in dd/MM/yyyy but i cant calculate using this format

Note: i cant change my form display format to mm/dd/yyyy cos i need it to be user friendly in my country ty (URGENT)

Once again thanks