Test Percentile Calculator
What percentile a score sits at — from a rank in a cohort, or from a score against a mean and standard deviation.
Two different questions share the word "percentile".
How the test percentile calculator works
Two different questions share the word "percentile". Given a rank in a known cohort it is a counting problem. Given a score against a distribution it is a normal-curve problem, and the answer depends on how many standard deviations from the mean the score sits.
The second is what standardised tests report, and it is why a small score difference near the mean moves you many percentiles while the same difference in the tail moves you almost none.
Formula: z = (score − mean) / SD; percentile = Φ(z)
Worked examples
| Inputs | Percentile from the distribution | Note |
|---|---|---|
| 78 against a mean of 65, SD 12 | 86.07% | 86th percentile |
| At the mean | 50% | 50th percentile exactly |
| Two SDs above | 97.72% | 97.7th percentile |
FAQFrequently asked questions
What is a percentile?
The share of the cohort scoring below you. The 86th percentile means 86% scored lower.
What is a z-score?
How many standard deviations a score sits from the mean. It is what makes scores from different tests comparable.
Why does the same point difference move me differently?
Because the normal curve is dense near the mean and sparse in the tails. Two marks near the middle can be several percentiles; the same two in the tail can be a fraction of one.
Is a percentile the same as a percentage?
No, and confusing them is common. Scoring 78% might put you at the 86th percentile, or the 40th, depending entirely on the cohort.
Does this assume a normal distribution?
The distribution-based figure does. The rank-based figure does not, which is why the two can disagree when the cohort is skewed.
Where these figures come from
- Brysbaert (2019), Journal of Memory and Language — How many words do we read per minute? — the 238 wpm silent reading rate, from 190 studies
- Office for Students — the regulator for English higher education
Last checked: September 2026. Reading and writing rates are from published meta-analyses, cited on the page.