z-score calculator

Convert a value into a z-score with normal-distribution probabilities and percentile.

z = (x − μ) / σ. Probabilities use the standard normal CDF (Abramowitz–Stegun approximation, error < 0.00001).

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How to use

  1. Enter the value, the mean, and the standard deviation.
  2. Read the z-score.
  3. Check the tail probabilities and percentile.

What it supports

z = (x − μ) / σ with σ > 0. Probabilities use the standard normal CDF via the Abramowitz–Stegun approximation (error < 0.00001). It assumes a normal distribution — heavy-tailed data needs a different model.

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