How to Remove Outliers in Excel

What this does

Excel has no outlier function, so flagging is a rule you choose and apply. The fence method marks anything more than 1.5 quartile-widths beyond the first or third quartile, and holds up on skewed data. The z-score method marks anything more than three standard deviations from the mean, and is easier to explain but weakens precisely when extreme values are present, because those values inflate the very standard deviation being used to judge them. The same idea underpins a lot of everyday Excel work, so the few minutes spent getting it right here pay back across every sheet you build afterwards. Treat it as a pattern, not a one-off, and it stops being something you look up and starts being something you reach for. Treat “remove outliers in excel” as a small repeatable workflow rather than a one-off click you hope to remember next time. Use a small test block before the live file, so any surprise in the affected cells shows up while it is still harmless. When a formula is involved, keep the inputs labelled beside it, reference cells instead of typing values, and apply number formatting only after the result checks out. That turns a data step that keeps your analysis trustworthy into a method you can reuse, explain, and defend when the workbook leaves your screen.

A worked example

With quartiles 12 and 27 the fences sit at 12 - 1.5×15 = -10.5 and 27 + 1.5×15 = 49.5. Put those in E2 and E3 and fill =IF(OR(A2<$E$2,A2>$E$3),"outlier","") down the column: the single 62 is flagged and everything else is left blank. One mistyped figure moves an average enough to change a decision, and a stated rule for flagging is what separates cleaning the data from choosing the answer. A practical tip before you scale it up: build it once on a small block of test data, confirm the number against the tool on this page, and only then point it at your real sheet. That one habit catches almost every mistake while it is still cheap to fix, long before a wrong figure reaches a report or a colleague.

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 or a download: the exact answer is at the top, and the detail below it is there for when you need it. That is the whole promise here — the answer first, and just enough context to make it stick. Here is the takeaway for “remove outliers in excel”: copy the answer if you are busy, but if you have a spare few minutes, rebuild the example in Excel yourself with the tool above open beside it. That single pass — type it, run it, watch the result move when you change an input — is what turns a formula you found into a technique you trust. Keep your inputs labelled and referenced, never hard-coded, and the same sheet stays correct and auditable as it grows. Done that way, you will not need to look this up again, and you will be the person others ask.

Common mistakes

• Deleting flagged rows without recording which and why, which makes the analysis impossible to reproduce.
• Applying the three-sigma rule to skewed data, where it flags almost nothing at one end and too much at the other.
• Treating an outlier as an error: a genuine extreme observation is often the most informative row in the table.
• Recomputing the fences from data that already had outliers removed, and then removing more.

Frequently asked questions