90th percentile: what it means and how to read it

How to read it

The value above which the highest tenth of the answers lie — a cut-off for "the top 10%".

In plain words

A hospital wrote down how long 200 patients waited. The manager wanted to promise patients a time, but did not know which time was fair. She asked for p90, the 90th percentile, and got 45 minutes. So nine patients in ten waited less than 45 minutes, and one in ten waited longer. Now she can say that most patients are seen within 45 minutes, and that a wait of 60 minutes belongs to the slowest tenth. The add-on counts it the way the program SPSS does, so the answer can differ a little from the PERCENTILE function in Google Sheets.

How it is computed

The value at the position (n + 1) · 90 / 100 of the sorted values, interpolated between neighbours (SPSS EXAMINE, HAVERAGE); before the first value — the minimum, past the last — the maximum.

Where you see it

• STATS_DESCRIPTIVE — Column-wise descriptive statistics with flexible metric selection and optional column filtering.

Related values

• Interquartile range — q3 − q1.
• Percentile — The q-th percentile, q from 0 to 100, fractions allowed (percentile.12.5); computed as in SPSS, like the quartiles. percentile.0.95 is the 0.95th percentile, not the 95th. Without q or with q outside 0…100 the cell is empty and the error is listed under the table.
• Median absolute deviation — The median of the absolute deviations from the median, without the 1.4826 factor.
• Geometric mean — The n-th root of the product of the values; zero and tiny values are raised to epsilon (Settings), a negative value gives an empty cell.
• Harmonic mean — n divided by the sum of 1/x; zero and tiny values are raised to epsilon (Settings), a negative value gives an empty cell.

Get it in your sheet

One formula in a cell gives the whole report, 90th percentile included. ALS Stats is a free add-on for Google Sheets™.

Install ALS Stats from Google Workspace Marketplace (opens in a new tab)