Written by Dackohn; last reviewed November 2026.
A percentile is a value: the 90th percentile is the score below which about 90% of the data fall. A percentile rank is a percentage: the share of the data at or below a score. Neither is the same as a percentage score. Scoring 70% on a hard test could put you at the 95th percentile.
Three terms that get mixed up
| Term | Question it answers | Example |
|---|---|---|
| Percentage | How much of the test did I get right? | You scored 70% |
| Percentile | What score is at this position? | The 90th percentile is 86.4 |
| Percentile rank | What position is this score at? | A score of 75 ranks at about 53 |
Worked example
Fifteen exam scores: 55, 62, 64, 68, 70, 71, 73, 75, 75, 78, 80, 82, 84, 88, 95.
The 90th percentile, inclusive method: position = 1 + 0.9 × (15 − 1) = 13.6, so go 60% of the way from the 13th value (84) to the 14th (88): 86.4.
Exclusive method: position = 0.9 × (15 + 1) = 14.4, so go 40% of the way from the 14th value (88) to the 15th (95): 90.8. This is the same data with a different, equally accepted definition.
The percentile rank of 75. Seven scores are below 75 and two equal it. The rank depends on how you treat the ties:
- Strictly below: 7 / 15 = 46.7%
- At or below: 9 / 15 = 60.0%
- Midpoint, counting ties as half: (7 + 1) / 15 = 53.3%
Using a normal distribution
When scores are roughly normal with a known mean and SD, you can convert with a z-score. On a test with mean 100 and SD 15, a score of 130 has z = 2, which is about the 97.7th percentile. See how to calculate a z-score and the z-table.
Named percentiles
The 25th, 50th and 75th percentiles are the first quartile, the median and the third quartile. See how to find quartiles.
Common mistakes
- Reading a percentile as a percentage correct. The 60th percentile on a hard exam might be 45% correct.
- Treating percentile gaps as equal. In a bell curve, moving from the 50th to the 60th percentile takes a much smaller score gain than moving from the 90th to the 99th.
- Averaging percentiles. Average the underlying scores instead.
- Saying “top 90th percentile”. The 90th percentile is the top 10%.
Try it yourself
Percentile Calculator →Both directions, by both Excel methods. Z-Score Calculator →Percentile from a z-score for normal data.Frequently asked questions
What is the difference between a percentile and a percentage?
A percentage is a share of a total, such as marks on a test. A percentile is a position relative to other people or values.
Is the 90th percentile good?
It means you are at or above about 90% of the group, whatever your raw score was.
Why do Excel functions give different percentiles?
PERCENTILE.INC and PERCENTILE.EXC use different position formulas. Both are valid, and they differ most in small samples.
Related reading: How to find quartiles and the IQR · The empirical rule · How to calculate a z-score
Sources & further reading: NIST/SEMATECH e-Handbook of Statistical Methods · OpenStax Introductory Statistics. How we compute & validate: methodology. Written & reviewed by Dackohn; last reviewed August 2026.