In Excel: select the range, then Home ▸ Conditional Formatting ▸ Highlight Cells Rules ▸ Duplicate Values, and pick a fill colour.
Select the cells to check (drag over B2:B20, or click a column header for the whole column).
On the Home tab, open Conditional Formatting ▸ Highlight Cells Rules ▸ Duplicate Values.
Choose a fill (e.g. Light Red Fill with Dark Red Text) and click OK.
To extend the check later, reselect a wider range and reapply, or edit the rule in Manage Rules.
What this does
Conditional Formatting colours repeated cells automatically, giving you an instant visual map of where duplicates sit — no formula and no helper column. The built-in Duplicate Values rule compares every cell in the selection and shades the ones that appear more than once. Because the rule is live, the colours update the moment you edit, paste or add data, so duplicates can never sneak back in unseen. Most people learn this as a sequence of clicks and forget it by next week; learning it as a pattern instead is what lets you apply it to the next, slightly different version of the problem without starting from scratch. That is the difference this page is trying to make. The difference between a quick fix and a sheet you can trust is the extra minute you spend validating “highlight duplicates in excel”. Start on a copy or a tiny sample, keep the affected duplicates visible, and compare the result with the tool above before you touch the real workbook. When this is a ribbon command, the selection matters more than the button: confirm the range, apply the command, then spot-check the output before saving. The point is a data step that keeps your analysis trustworthy, but the practical win is that someone else can open the file and understand what happened without asking you.
A worked example
You have customer emails in B2:B20. Select that range, go to Home ▸ Conditional Formatting ▸ Highlight Cells Rules ▸ Duplicate Values, and choose the red fill. Every email that appears twice — say jo@acme.com sitting in B4 and B17 — turns red in both cells, while one-off addresses stay white. Type a new repeat and it reddens instantly. When you want to see duplicates at a glance during data entry or review — spotting a double-booked email or a repeated invoice number on screen — coloured cells beat any formula, because the eye catches them instantly and the rule keeps watching as you type. If there is any chance you will reuse this, drop it into a small template tab right now: a labelled input area on the left and the formula beside it, checked once against the tool above. Next time the same question comes up, the answer is a single paste away instead of a rebuild from memory.
In Google Sheets
Google Sheets handles this almost identically to Excel. The formula syntax above is the same, and the menu lives under a slightly different label rather than a ribbon tab. Use the platform toggle at the top of the page to switch every keyboard shortcut between Windows and Mac, and expect at most cosmetic differences in naming. Nothing on this page is behind a login: the tool runs entirely in your browser, the formula is shown in full with one-click copy, and the steps work the same on Windows and Mac. That is the whole promise here — the exact answer, a way to prove it on your own numbers, and just enough context to make it stick. Treat “highlight duplicates in excel” as a small building block rather than a chore. Once the inputs sit in their own cells and the formula reads from them, the same setup answers a dozen related questions with a tweak, and Excel keeps every dependent figure current as the data changes. The tool above is there so you can rehearse and verify before committing anything to a real workbook; the steps and worked example are there so the logic sticks. Get it right once and it stops costing you time — it starts saving it, every time the question comes back around.
Common mistakes
- Selecting one column when duplicates should be judged across several — the rule only compares the cells you highlight.
- Expecting the colour to remove anything; highlighting is purely visual, deletion is a separate step.
- Leaving the selection too small, so duplicates outside the range never get coloured.
- Confusing "Duplicate Values" with "Unique" in the same dialog — the dropdown switches between colouring repeats and colouring one-offs.
Frequently asked questions
How do I highlight whole rows, not just cells?
Use a formula rule instead: New Rule ▸ Use a formula, enter =COUNTIF($B:$B,$B2)>1 and apply the fill to the whole row range.
Can I highlight duplicates in one colour and uniques in another?
Yes — add two rules: one Duplicate Values rule and one Unique Values rule, each with its own fill.
How do I clear the highlighting?
Home ▸ Conditional Formatting ▸ Clear Rules removes the colouring without touching your data.
Other ways people ask this
People reach this page typing “excel highlight duplicates”, “how to highlight duplicate in excel”, “how do i highlight duplicates in excel” and “how do you highlight duplicates in excel”, among other phrasings; whichever wording you used, the fix above is the one you want.
Why do people search for this in so many different ways?
Because the same task has many names. “excel highlight duplicates”, “how to highlight duplicate in excel”, “how do i highlight duplicates in excel” all point at the one operation explained on this page, which is why they all lead here.