Percentile Calculator
Enter a data set and either a target percentile (to find the value at that percentile) or a specific value (to find its percentile rank within the set).
How the Percentile formula works
Value at a given percentile (linear interpolation method):
rank = (percentile / 100) × (N − 1) value = sorted[floor(rank)] + (rank − floor(rank)) × (sorted[floor(rank)+1] − sorted[floor(rank)])
Percentile rank of a value works in reverse: it's the percentage of data points less than or equal to that value.
Step-by-step calculation
- Sort the data set from smallest to largest.
- Convert the target percentile into a fractional rank position within the sorted list.
- If the rank falls between two data points, interpolate linearly between them.
- The interpolated value is the result at that percentile.
Worked example
Data set: 3, 7, 8, 12, 15, 21, 25 (7 values). The 50th percentile (median): rank = 0.5 × 6 = 3, which lands exactly on the 4th sorted value (index 3): 12. The 90th percentile: rank = 0.9 × 6 = 5.4, interpolating between the values at index 5 (21) and index 6 (25) gives 21 + 0.4×(25−21) = 22.6.
Frequently asked questions
Is there more than one way to calculate percentiles?
Yes — this calculator uses linear interpolation (the method Excel's PERCENTILE.INC and most statistics software use by default), but a 'nearest rank' method is also common and can give slightly different results, especially in small data sets.
What does 'being in the 90th percentile' mean?
It means a value is greater than or equal to 90% of the other values in the data set — a common way to express relative standing, like in test scores or growth charts.