u/Infamous_Review_9700

I've been investigating why some Excel workbooks become painfully slow even when they don't contain that much actual data.

A few things I've found surprisingly easy to overlook:

• Whole-column references like A:A can make formulas process far more cells than the workbook actually needs.
• Volatile functions such as OFFSET and INDIRECT can trigger additional recalculation.
• A workbook can have a huge used range even when the visible data occupies only a tiny portion of it.
• Broken references can be hiding in places you don't immediately notice.
• External links, add-ins, and macros can introduce another layer of slowdown.

The phantom used-range problem surprised me the most. A sheet can look like it contains only a couple of cells while Excel's tracked range extends thousands of rows and columns beyond the actual content.

I'm curious what other people have encountered:

What's the strangest or least obvious thing you've found that was making an Excel workbook slow?

I'm especially interested in cases where the workbook looked completely normal but had some hidden performance problem.