Not every test uses z
This calculator is for z-score normal approximation only. t-tests, chi-square tests, binomial tests and regression models need their own assumptions and degrees of freedom.
Example
A z-score of 1.96 gives a two-tailed p-value of about 0.05 under the standard normal distribution.
Common mistakes
Choose one-tail only when the hypothesis was directional before looking at the data. Switching tails after seeing the result makes the p-value misleading.
Limitations
A p-value is not the probability that the null hypothesis is true. It depends on the test design, assumptions, sample size and chosen statistical model.
Last reviewed: 2026-05-17