Best Architectural Solution for a Centralized Excel Add-In?

[mdershewitz]

Perhaps I'm not asking the right question exactly, but here goes. My firm currently produces a somewhat tedious and definitely repetitive calculation, that we currently produce in Excel files from data file inputs that are copied over spreadsheet-to-spreadsheet. However, 1) all of these spreadsheets should be based on the same data, and 2) it would be nice to have a central place in the cloud where we can update the input data across all spreadsheets.

With that said, what is the best solution to this? Having a centralized input sheet would help. I was also thinking about developing a custom Excel-add in that can be called as a function from Excel each time the calculation is needed. How would one begin building this kind of add-in that turns machinations in individual spreadsheets to a function call that can be used across all spreadsheets (without localized macros?)

Thanks!
Mike