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Z-Score Calculator

Calculate a z-score and see where a value falls within a normal distribution.

Results update as you type.

Z-score

2

About the 98th percentile (normal distribution)

Percentile (approx.)
98.5%
Standard deviations from mean
2
Z-score2

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Quick answer

A score of 130 where the mean is 100 and SD is 15 gives z = 2 — about the 98th percentile.

How it works

A z-score says how many standard deviations a value is above or below the mean. On a normal curve, z = 0 is the 50th percentile, z = 1 is about the 84th, z = 2 about the 98th.

Formula

z = (value − mean) ÷ standard deviation

Assumptions & limitations

  • Percentile assumes a normal distribution.

Frequently asked questions

Is a high z-score good?

It depends on context — high is great for test scores, but not necessarily for things like error rates.