What I've devised based on @Pecoflyer 's 3D-referencing post works, but it is rather cumbersome.

I appreciate the effort you put into your post. And your solution appears more elegant than my rendition -- but quite beyond my Excel literacy.

Before I attempt to educate myself on Excel defined tables and Validation lists, would you take a moment confirm that your solution should work for my project?

My daughter is a residential construction contractor. I want to estimate her working capital needs by month based on her budget for each "job".

Under my "3D-reference" solution, each job resides on its own sheet. And each job "cell" is an amount by [row] job phase (e.g. Demo, Concrete, Masonry ...) and [column] month staring with January for 24 columns.

Additional rows include "Billing", so as to calculate additional rows "Net" and "Cumulative".

Additional columns include "Phase name" and "Balance Forward"

The "Totals" sheet accumulates all the job sheets (along with other calculations) to establish working capital requirements by month.

My solution works. And serves to meet this month's deadline. So under the adage "If it ain't broke ..." I should probably leave it alone.

But your solution intrigues me. Am I correct that your approach is likely better?