Remove Duplicates Deleted the Wrong Rows / Too Much Data

What actually happened

Remove Duplicates compares rows only on the columns you leave checked in its column list. If your data has an Order ID column that was left unchecked, two completely different orders that happen to share the same Customer Name and Date will be treated as duplicates of each other — and Excel deletes all but the first one it encounters, with no warning about what made them match.

Why the dialog is easy to get wrong

Excel remembers which columns were checked or unchecked the last time you used Remove Duplicates on that workbook. If you ran it before on a different, narrower selection of columns, that same narrower selection is what's checked by default the next time — even if your current selection includes more columns you meant to compare on.

Recovering the data

If you catch it immediately, Ctrl+Z undoes it completely — Remove Duplicates is a single undoable action. If you've since saved or closed the file, you'll need a backup or an earlier version (AutoRecover, a cloud version history, or an export you ran before) to get the deleted rows back; there's no way to “undelete” from inside the reduced file itself.

Getting it right the next time

Before running Remove Duplicates, identify the column or combination of columns that actually makes a row unique in your data — usually an ID field — and check only those (plus any others you specifically want to require an exact match on). Upload your file below to preview exactly which rows would be treated as duplicates under a chosen set of columns before anything gets deleted.