P value calculator
Enter a calculated test statistic, choose its reference distribution and select the direction of the alternative hypothesis.
How do I use this page?
- Select the statistic distribution.
- Enter the statistic, tail and any required df.
- Read p and compare it with a preselected alpha.
What this page does not do: This tool converts an existing Z or t statistic. It does not verify the test assumptions or how the statistic was obtained.
Further reading
Theory — what is a p-value in a statistical test?
A p-value is the probability of getting a test statistic at least as extreme as the one calculated, assuming the baseline hypothesis is true. The calculator needs a computed test statistic, its reference distribution and the direction of the alternative hypothesis. A two-tailed test counts both tails, so it usually gives a larger p-value than a one-tailed test. A low threshold like 0.05 says nothing about an effect's practical size, and a p-value never proves the baseline hypothesis is true.
Frequently asked questions
Does p < 0.05 prove an important effect?
When should I use a two-sided test?
See also
A/B test calculator
Compare two proportions in an A/B test. Calculate conversion rates, difference, uplift, z score, p value and c
A/B test planning — sample size, MDE and duration
Plan a two-proportion experiment, estimate detectable effect and traffic duration.
ACF and PACF autocorrelation calculator
Calculate ACF and PACF across time-series lags. Review the chart, reference bounds and coefficient table.