Interquartile Range Formula Excel

What this does

QUARTILE splits a dataset into four equal parts, returning the value at whichever boundary you request. Its second argument is an index from 0 to 4, not a percentage, which trips people who come to it from PERCENTILE. Its practical value is the interquartile range: quartile 3 minus quartile 1 gives the spread of the middle half, and the standard outlier rule flags anything beyond 1.5 IQRs outside those bounds. That is also exactly what a box plot draws, so QUARTILE is how you replicate one numerically. 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. The difference between a quick fix and a sheet you can trust is the extra minute you spend validating “interquartile range formula excel”. Start on a copy or a tiny sample, keep the affected formula visible, and compare the result with the tool above before you touch the real workbook. 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. The point is a calculation you can defend to a CFO or an auditor, but the practical win is that someone else can open the file and understand what happened without asking you.

A worked example

Order values in B2:B200: =QUARTILE.INC(B2:B200, 1) and =QUARTILE.INC(B2:B200, 3) give the quartile bounds, and their difference is the IQR. An upper outlier threshold is =QUARTILE.INC(B2:B200,3) + 1.5*(QUARTILE.INC(B2:B200,3)-QUARTILE.INC(B2:B200,1)). QUARTILE is the numeric basis of the box plot and the standard outlier rule, which makes it the fastest way to describe spread without assuming a distribution. 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 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. The short version of “interquartile range formula excel”: the answer is at the top of this page, the tool proves it on your own numbers, and the sections above explain why it holds so the next variation does not stump you. Excel rewards people who reference cells instead of typing values and who keep inputs separate from formulas, because that is what makes a result you can audit months later. Build it once, deliberately, with the live tool as a check, and you convert a one-off lookup into a reusable skill — which is the whole point of learning the why and not just the what.

Common mistakes

• Passing 0.25 instead of 1 — the argument is an index from 0 to 4, not a proportion.
• Using QUARTILE.EXC on small samples where the boundary is undefined, which returns #NUM!.
• Reporting quartiles on a tiny dataset, where they are unstable and a simple sorted list says more.

Frequently asked questions