It is possible to make the Sum Excel formula reference another sheet, or multiple sheets, and add up a range of cells across those sheets.

A complex Excel 2007 workbook could require multiple sheets. By default, Microsoft provides three sheets on each workbook, but you can add as many as you need. Clicking the "Insert Worksheet ...

Inserting a lot of columns or rows in Microsoft Excel is awkward and prone to mistakes. When you need to enter dozens or more columns, use this VBA procedure for ease and accuracy.