Question 1

How do you calculate a z-score?

Accepted Answer

A z-score is z = (x − μ) / σ, where x is the value, μ is the mean, and σ is the standard deviation. It tells you how many standard deviations a value is from the mean.

Question 2

How do you find probability from a z-score?

Accepted Answer

Use the standard normal CDF Φ(z). P(X < x) = Φ(z), and P(X > x) = 1 − Φ(z). This calculator evaluates the normal CDF for you and reports the percentile.

Question 3

What is a good or normal z-score?

Accepted Answer

About 68% of values fall within z = ±1, 95% within ±2, and 99.7% within ±3. A |z| above 2 or 3 is unusual for a normal distribution.

Z-Score & Normal Distribution Calculator

Inputs