Standard sequential order of numbers in multiple text boxes.

I need a code and or formula to help me get a sequential order of numbers in multiple text boxes. In theory it is relativity simple: Field 1 (CD Day 1 as I call it) + 1 = Value Needed. I was able to get the dates to propagate in order properly but of course that coding if specific to dates. Any help is appreciated. Thank you!

PS- I don't need numbers added together but I need the next number in line to automatically popup when the initial number gets put in.