VBA _Change() command Question

When I use that function on a UserForm it executes the code immediately, not waiting for the value to be entered.

Thus the code executed that relies on the new values returns an incorrect value.

Example

A1 | 150
A2 | 100 <-- this is the value being changed to 300 with the Textbox
A3 | 250 = Sum(A1:A2)

Now with:

Private Sub TextBox_Change() 

    Range("B3").Value = Range("A3").Value

End Sub

it copies over the value of 250 while I'm changing the value to 300...

Is there a way to get it to wait till I'm done changing the value first?