Statistics Utility
P-Value Calculator
Calculate left-tailed, right-tailed, or two-sided p-values from a z statistic or Student t statistic.
Method
For a z statistic, the calculator uses the cumulative distribution function of the standard normal distribution. For a Student t statistic, it uses the Student t distribution with the degrees of freedom you provide. A left-tailed p-value is the CDF at the statistic, a right-tailed p-value is one minus the CDF, and a two-sided p-value is twice the smaller tail probability.
Worked example
For z = 1.96 with a two-sided alternative, the result is approximately 0.0500. For t = 2.262157 with 9 degrees of freedom, the two-sided result is also approximately 0.05.
When this is useful
Useful when a hypothesis test already provides a valid z or t statistic and you need the corresponding tail probability.
Privacy
The values you enter into this calculator are processed in your browser by Practical Tools Hub application assets. The calculator does not need to send your calculation inputs to a third-party calculation service.
Limitations
A p-value is meaningful only under the statistical model and test that produced the statistic. This tool does not decide which hypothesis test is appropriate, does not check independence or distributional assumptions, and does not turn a p-value into an effect size or probability that a hypothesis is true.