How to Use the Percentile Calculator

Enter your data values separated by spaces or commas. Choose the type of analysis: find a percentile value, calculate a percentile rank, analyze quartiles, or compute deciles.

Understanding Percentiles

Percentile Values

A percentile indicates the value below which a given percentage of data falls:

50th percentile: The median (50% of data is below)
25th percentile: First quartile (Q1)
75th percentile: Third quartile (Q3)
90th percentile: Only 10% of data exceeds this value

Percentile Rank

The percentile rank tells you what percentage of data falls at or below a specific value. Useful for comparing individual values to a distribution.

Quartiles and IQR

Q1 (25th percentile): Lower quartile
Q2 (50th percentile): Median
Q3 (75th percentile): Upper quartile
IQR = Q3 - Q1: Interquartile range (middle 50% spread)

Outlier Detection

Uses the 1.5 × IQR rule:

Lower fence: Q1 - 1.5 × IQR
Upper fence: Q3 + 1.5 × IQR
Values outside these fences are considered outliers

Deciles

Deciles divide data into 10 equal parts:

D1 (10th percentile): 10% below
D5 (50th percentile): Median
D9 (90th percentile): 90% below

Calculation Method

This calculator uses linear interpolation (similar to Excel's PERCENTILE.INC function). For a percentile p in a dataset of n values:

Calculate index = (p/100) × (n-1)
Interpolate between adjacent values if needed

Common Applications

Academic grading and standardized testing
Growth charts in pediatrics
Income and wealth distribution analysis
Performance benchmarking
Quality control and process analysis
Data exploration and summary statistics

Important Notes

Different methods exist for calculating percentiles
Results may vary slightly between statistical software
More data points give more reliable percentile estimates
Percentiles are useful for non-normal distributions