I have what I think is a simple spreadsheet, about 60 columns and 30 lines,
in each of 3 tabs.

My second and third tabs are just where I dump exported data from another
program. No formulas, just raw numbers with minimal formating.

My first tab is where I summarize my dumped data. I use a combination of
SUMIFs (to match up imperfect column alignment, like to match column months,
etc.) on a lot of the data. (The data columns are months 1-60, rows are
account categories.) I also use INDEX and column numbers to point to
specific numbers, plus also a few lines of MATCH in order to grab the correct
line for some categories.

Anyway, this simple workbook is very sluggish. When I want to insert rows,
copy formulas across, etc., it moves very slow, sometimes to the point where
it seems to freeze and I either leave it alone for 20 minutes or I have to
End Task and reopen Excel. I've started stripping out the MATCH and INDEX
formulas (going back to manual pointing), but keeping my SUMIFs, and still it
is very slow.

The workbook is about 11 Mb, with no graphics.

Question (finally!): Are these formulas memory hogs? Should I use them
sparingly? Could something else be wrong?

Thanks for your help.