A workbook with live formulas, cross-sheet references, and maybe a macro or two is not something you want to run through a random online tool and hope for the best. Reasonable caution — here’s exactly what happens.
Compress Excel does exactly one thing: it re-encodes embedded images — screenshots, logos, pasted photos — to a smaller, screen-appropriate size. That’s the entire operation. Every cell value, every formula, every named range, every conditional formatting rule, every pivot table’s data connection is left byte-for-byte as it was, because the compressor never opens or touches the calculation engine at all — it only reaches into the parts of the .xlsx file that store pictures. This is checkable, not just a claim: open the compressed file afterward and every formula still shows its original expression in the formula bar, still recalculates from its original references, and still updates correctly if you change an input cell. Nothing about how the spreadsheet works changes, only how much space its pictures take up.
If your workbook is large mainly because of a PivotTable cache, heavy formatting applied to entire columns, or bloated external data connections rather than embedded images, compression won’t make much of a dent — those aren’t image data, so there’s nothing for an image compressor to act on. That’s not a limitation worth working around with a more aggressive setting; it means the size is coming from somewhere else entirely, and the fix is different. Why Is My Excel File So Large? covers how to find and clear each of those specifically.
The one format that needs a second look is macros. A workbook containing macros has to be saved as .xlsm, not .xlsx — a different, related format Excel treats distinctly for security reasons. Compressing a normal .xlsm file works exactly the same way and preserves the macro code untouched, since macros live in a separate part of the file structure from both the images and the worksheet data. The one thing worth verifying yourself: after downloading, confirm the file still has the .xlsm extension, or that your compressed download opens with “Enable Content” prompting you for macros, if your email or browser renamed the extension in transit — a macro-enabled file that got silently renamed to .xlsx by something in the pipeline would show blocked or missing macros not because compression removed them, but because the file type changed.
If you want to double-check before trusting it with an important file, it takes four steps: note a formula result or two, and the file size, before compressing; run it through Compress Excel; open the result and confirm the same formulas produce the same values, and that any macros still run; then compare the file size, which tells you how much of the original bloat was actually images.
Afterward, if the file still needs to shrink further, check for pivot table cache and column-wide formatting — see Why Is My Excel File So Large?. And if the destination only needs to view the numbers, not recalculate them, Excel to PDF sidesteps the size question differently — a PDF of the same content is usually smaller still, and nobody can alter your formulas by accident.
The free Compress Excel tool does exactly what’s described above and nothing more — no login, no watermark, file removed from our servers right after.