Z-Score Calculator
Last updated: November 5, 2026
Calculate a z-score, deviation from the mean and approximate normal-distribution percentile.
Z-score
—
- Deviation from the mean: —
- Approximate percentile: —
- Position relative to mean: —
On this page
Quick summary: Calculate a z-score, deviation from the mean and approximate normal-distribution percentile.
Read the complete guide
Updated reference sections in this guide are in English.
What this calculator estimates
Calculate a z-score, deviation from the mean and approximate normal-distribution percentile.
How to use it
Enter Observed value; Population mean; Standard deviation. Select Calculate to update the results.
How the calculation works
The z-score is the observed value minus the mean, divided by the standard deviation.
Worked example: starting scenario
| Observed value | 85 |
|---|---|
| Population mean | 70 |
| Standard deviation | 10 |
| Z-score | 1.5 |
|---|---|
| Deviation from the mean | 15 |
| Approximate percentile | 93.3193% |
| Position relative to mean | Above the mean |
Important limitations
The percentile is an approximation that assumes a normal distribution.
The sign identifies which side of the mean
A value of 60 with mean 70 and positive standard deviation 5 has z = −2. A value of 80 has z = +2. The standard score itself uses only (value − mean) / standard deviation. Interpreting the percentile as an actual population percentile additionally assumes a normal distribution; a z-score alone does not establish that distribution.