P-Value Calculator

Use this P-value calculator to compute exact tail probabilities for common test statistics. This calculator supports Z-scores, t-scores, chi-square (χ²), and F-scores. To use it, select your test statistic from the dropdown menu. Then, enter your degrees of freedom (if required) and observed test statistic value. Click Calculate to see the result.

For Z and t-tests, you can choose two-tailed, left-tailed, or right-tailed p-values. This P-value calculator always reports right-tailed probabilities for chi-square and F distributions. (See below for details.) Below the calculator, you’ll find more information about how it works and how to interpret the results. See all my Statistical Calculators!

Interpret the p-value as the probability of obtaining a result at least as extreme as the observed results when you assume the the null hypothesis is true. For a more detailed explanation of what it does and doesn’t mean, read my article Interpreting P-values.

Compare the p-value that this calculator produces to your significance level to determine whether the results are statistically significant. If your p-value is less than your significance level, you can reject the null hypothesis.

For more information about how this p-value calculator works, read my article about How to Find the P value: Process and Calculations.

In this p-value calculator, you must choose a one- or two-tailed test for Z- and t-scores. Usually, the default choice of a two-tailed test is best. Learn more in-depth in my post, One- and Two-Tailed Tests Explained.

Only Right Tailed P-values for Chi-Square and F-values

This P-value calculator produces only right-tailed p-values for chi-square and F distributions because both statistics measure the magnitude of deviation or variance—never its direction. These distributions are bounded at zero and skewed right, so they don’t support negative values or symmetric tails. In a chi-square test, you sum squared differences between observed and expected counts. In an F-test, you calculate a ratio of sample variances. Both tests determine whether your observed statistic exceeds a critical threshold, making them fundamentally one-sided.

Because these tests accumulate only positive quantities—squared deviations or variance ratios—large values signal evidence against the null hypothesis. Small values indicate a better fit or smaller variance and do not contradict the null. As a result, the only relevant area of extremity lies in the right tail. This P-value calculator reflects that by reporting the probability of obtaining a value at least as extreme as the one you entered, based on the right tail of the distribution.