Shrink Excel

Yes. Compressing a workbook needs a server, so the file is sent over an encrypted connection. The copy there is deleted as soon as the result is sent back, unless you are signed in and asked to keep it.

It depends on what is inside, and no amount is promised. A workbook with large pictures can shrink a lot at Balanced or Strong. One that is mostly text and numbers is already compact and often shrinks by only a few percent. The result dialog shows the real sizes before and after.

You get your original file back, unchanged, and the dialog says no reduction was made. A larger file is never returned.

No. Sheets, cells, formulas, styles, charts, names, pivot tables and every other part of the workbook other than pictures are copied exactly. Only the file packing changes, plus the pictures at Balanced and Strong.

Lossless leaves every picture as it is and only stores identical copies once. Balanced and Strong re-encode JPEG and PNG pictures in their own format at about 150 or 110 dpi for the size they are shown, never larger than they were, which loses some detail. PNG transparency is kept. Cropped, grouped and chart pictures are left alone.

Only .xlsx. Macro-enabled .xlsm, digitally signed, password-protected and legacy .xls workbooks are refused with the reason, not returned half-processed.

Yes. It runs on a server rather than in your browser: up to 25 MB per file.