Formula in filtered column

Andrew_Hinson 

Assuming I am following you, what you're doing and what you want to do, I have a couple of thoughts. First, let me say that I track my finances in a somewhat similar way. And I've learned--assuming you have all these rows and rows of transactions as a legitimate Excel Table--...I've learned that putting formulas into columns in Tables can be tricky unless you are wanting that same formula to be applicable to every row. So be careful, whatever you do.

That said, for this particular need, I would recommend trying what we often call a "helper column," which is to say, do not try to have this added 14 days applied in the same column as the dates for all the other transactions. Instead, have a separate column that tracks what might be called "AdjustedDates" and put the formula there that finds the last date used for that category and then adds 14 to it. You could make that formula particularly smart and have it just copy all other dates as they are, and then that AdjustedDates column becomes the one you use in a Pivot Table, say, if you use that to create monthly reports.

I have a formula I've created that does more or less what I'm suggesting, finding the last date when the category appeared. (You might need to play around to make sense of this; I'm assuming you have that ability.) The XMATCH portion is key, and the -1 there at the end is the key to the key: it is what finds the last match in the column, as opposed to the first, which is what we generally use MATCH and XMATCH to do.

=INDEX([DatesColumn],XMATCH("Category",CategoryColRefs,0,-1))