P-Value Calculator (z, t, chi-square)
Get the p-value for a z-score, t-statistic or chi-square statistic — one- or two-tailed — and check it against your significance level.
How to use
- 1Choose the test statistic type and enter its value.
- 2Enter degrees of freedom for t and chi-square tests, and choose the tails.
How it's calculated
z: p = 1 − Φ(|z|) per tail. t: uses the Student's t distribution with df degrees of freedom. Chi-square: p = 1 − CDF(χ², df) (right tail).
Frequently asked questions
One-tailed or two-tailed?
Two-tailed tests any difference; one-tailed only a difference in the direction you predicted beforehand. Two-tailed is the safer default.
What does p < 0.05 mean?
If the null hypothesis were true, results at least this extreme would occur less than 5% of the time. It's not the probability the hypothesis is true.
Why is chi-square always right-tailed?
The chi-square statistic measures deviation, so only large values are evidence against the null hypothesis.