ARRAYFORMULA does not increase cell as it expands

Solution 1:

Your sample spreadsheet is still "View only"; so neither I nor anyone else can directly leave our solutions. However, place the following formula in D1:

=ArrayFormula({"Difference"; IF(A2:A="",,IFERROR(A2:A-OFFSET(A2:A,-1,0)))})

This will create the header (which you can change within the formula itself as you like) and all results.

(Adjusting to the location in your actual spreadsheet, as indicated in your post, this would be =ArrayFormula({"Difference";IF(L7:L="",,IFERROR(L7:L-OFFSET(L7:L,-1,0)))}).)

Solution 2:

Couple Comments

You should accept Erik Tyler's answer as he put in more work and helped you present your problem more clearly. However these formulas allow for some more flexibility if you want any values below the rows (which now that I think about it doesn't make a lot of sense based on having a dynamic array flowing down, but conceptually maybe someone will find it useful).

Simple Formula will require one cell below your range to be blank:

=iferror(filter(filter(N(A2:A),A2:A<>"")-N(A1:A),A1:A<>""),"")

Complex Formula will allow values directly below (which I again admit seems nonsensical considering the whole point of this is a dynamic expansion down rows...)

=Filter(filter(filter(N(A2:A),A2:A<>"")-N(A1:A),A1:A<>""),ISNUMBER(filter(filter(N(A2:A),A2:A<>"")-N(A1:A),A1:A<>"")))

I gave a demo on your page.