Stop copying and pasting the same numbers every month
If you keep separate sheets for each month or each category and manually copy totals into a summary sheet, that summary goes stale the moment the source data changes. Building a live cross-sheet reference instead means the summary updates itself the moment anything upstream changes, with zero extra work on your part.
It also works across multiple sheets at once
A single formula can pull from several sheets in one calculation -- for example, a SUM formula written across a 3-D reference like "=SUM(Jan:Dec!B2)" adds up the same cell from every sheet between January and December, which is a natural next step once basic cross-sheet references feel comfortable.
Frequently Asked Questions
What happens if a sheet name has a space in it?
Excel automatically wraps sheet names that contain a space in single quotes, so the formula shows something like "='Jan Sales'!A1". If you are typing the reference by hand, keep that same format.
Can I reference a sheet in a different workbook file?
Yes. With both files open, follow the same steps and click the sheet and cell in the other file -- Excel builds a formula that includes the file name so it keeps pointing to the correct source.