# IQ Percentile Calculator

URL: https://speedycalculator.com/calculators/health/iq-percentile/
Last updated: 2026-10-30

> The IQ percentile calculator converts an IQ score into a percentile – the share of people with a lower score – and the classification used on Wechsler tests, assuming IQ follows a normal distribution with mean 100 and SD 15. Type a percentile to get the matching IQ.

## Inputs

- IQ score
- Standard deviation of the test

## Results

- Percentile
- z-score
- One in
- Wechsler classification

## Formula

```
z = (IQ − 100) ÷ 15
Percentile = Φ(z) × 100
Rarity: 1 in 1 ÷ (1 − percentile)
```

## Explanation

IQ tests are scaled so that the average is 100 and two-thirds of people score between 85 and 115. About 2% score 130 or above, the usual threshold for giftedness, and about 2% below 70.

### How to use the IQ Percentile Calculator

- **IQ score**
- **Standard deviation of the test**
- Every result field is editable: type into **Percentile** and **IQ score** plus every other field update to match.

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the IQ score (most modern tests use SD 15; Stanford–Binet editions before 2003 used 16, Cattell 24).

### Tips

- Measure lying length for babies under 2 and standing height from age 2.
- Use the exact age in months for babies – a few weeks matters.
- Follow the trend across several visits; crossing two major percentile lines is more important than one value.
- Discuss concerns with your paediatrician.

### Common mistakes to avoid

- Comparing a baby with the wrong sex chart.
- Reading the 50th percentile as "normal" and everything else as abnormal.
- Using corrected age incorrectly for premature babies.

### Inputs explained

FieldWhat to enterIQ scoreA numberStandard deviation of the testA number

### What each result means

- **Percentile** = ncdf(([IQ score] - 100)÷[Standard deviation of the test])×100
- **z-score** = ([IQ score] - 100)÷[Standard deviation of the test]
- **One in** = 1÷(1 - [Percentile]÷100)

### Example values

How the main result changes when **IQ score** changes and everything else stays at the example values above:

IQ scorePercentile (%)600.49025.212090.9150100180100
*Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.*

## Worked example

Inputs — IQ score: 120; Standard deviation of the test: 15.

Results — **Percentile = 90.9 %**; z-score = 1.33; One in = 11; Wechsler classification = Superior.

## Key terms

- **z-score**: Number of standard deviations from the mean.

## FAQ

**What is an average IQ?**
100, with 90–109 classed as average.

**What percentile is an IQ of 130?**
About the 98th percentile.

**Is IQ fixed?**
It is fairly stable in adulthood but can change with education and environment.


## Sources

- Wechsler D. Wechsler Adult Intelligence Scale – Fourth Edition, technical manual. Pearson, 2008