How it works
Compute the right-tail and two-sided p-value from a z, t, or chi-square test statistic.
Choose a test statistic, enter its value, and (for t and chi-square) the degrees of freedom. The calculator evaluates the corresponding cumulative distribution and reports the right-tail and two-sided p-values.
Formula
z: p = 1 − Φ(z). t: p = 1 − T(t, df). χ²: p = 1 − F(x, k). Two-sided = 2 × min(Φ(z), 1 − Φ(z)) for z (analogous for t).
z/t/χ²- Test statistic value (number)
df- Degrees of freedom (integer)
Examples
- z = 1.96z · statistic 1.96right-tail ≈ 0.025 · two-sided ≈ 0.050
Frequently asked questions
What is a p-value?
The probability, under the null hypothesis, of observing a statistic at least as extreme as the one computed.
Which tail should I use?
Use the two-sided value for '<>' alternatives and the right-tail for '>' alternatives.
How to read the result
A small p-value (commonly below 0.05) suggests the result is unlikely under the null hypothesis; a large value means it is consistent with it.
Limitations
Assumes the standard theoretical distributions and valid test assumptions. It reports probabilities, not the correctness of your experiment design.
Source: Standard normal, Student's t, and chi-square cumulative distributions computed numerically.