Question 1

What is a p-value?

Accepted Answer

A p-value is the probability of obtaining test results at least as extreme as the observed results, assuming the null hypothesis is correct. A small p-value (typically ≤ 0.05) indicates strong evidence against the null hypothesis.

Question 2

How do I calculate a p-value from a Z score?

Accepted Answer

For a two-tailed test, the p-value equals 2 × (1 - Φ(|Z|)) where Φ is the standard normal CDF. For a one-tailed test, it is 1 - Φ(Z) for right-tailed or Φ(Z) for left-tailed. Enter your Z score and select the tail type.

Question 3

What p-value threshold should I use?

Accepted Answer

The most common significance level (alpha) is 0.05. If p ≤ 0.05, the result is considered statistically significant. Other common thresholds are 0.01 (highly significant) and 0.10.

Question 4

Is this p-value calculator free and private?

Accepted Answer

Yes, this tool is completely free and runs entirely in your browser. No data is sent to any server — your calculations are 100% private.