How percentile rank calculator works
A percentile rank answers one question: what fraction of the data sits at or below this value? If your score is at the 90th percentile, 90% of test-takers scored no higher than you. The calculation is pure counting — sort the data, count how many values fall below the target (and how many tie it), and divide by the total. No bell curve, no assumptions about the data's shape: the percentile rank is a direct description of the sample you give it.
The one subtlety is ties. With scores 2, 4, 4, 4, 5, 5, 7, 9, what percentile is the value 5? Four values are strictly below it (50%), six are at or below it (75%), and the midpoint convention — which splits the tied pair — puts it at 62.5%. All three answers are used in textbooks and software, so this tool reports all three side by side rather than silently picking one: strictly below, at or below, and the midpoint (below plus half the ties).
The tool also shows the counts behind the percentages, the 1-based position of the value in the sorted list, and the sorted data itself so you can verify the ranking by eye. Typical uses include test scores, growth charts, income distributions, latency measurements, and any ranking where 'how high is this compared to the rest?' matters more than the raw number.