Question 1

How do I calculate a p-value from a z-score online?

Accepted Answer

Enter your z-score, choose left-tailed, right-tailed, or two-tailed mode, and the calculator instantly returns the matching probability from the standard normal distribution.

Question 2

What does a two-tailed p-value mean in this calculator?

Accepted Answer

A two-tailed p-value doubles the smaller one-sided tail area, so it measures how unusual your z-score is in either direction away from zero.

Question 3

Is this z-score calculator private?

Accepted Answer

Your z-score calculations run locally in browser memory. This site also loads analytics that may collect standard page and device metadata, but the calculator does not send your input away for computation.

Question 4

Why can a very small p-value appear in scientific notation?

Accepted Answer

Very small probabilities are shown in scientific notation to preserve readability while still reflecting the tiny tail area associated with an extreme z-score.