P-value calculator
Enter the statistic from your test and the test type to get the chance of a result this extreme if the null hypothesis is true.
Loading the tool…
Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter statistic, test statistic, degrees of freedom (for t) and test type.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Two-tailed: p = 2 × P(T > |x|). Right: p = P(T > x). Left: p = P(T < x). T is the standard normal or Student t with the given degrees of freedom.
Example
Inputs: Statistic = z (normal), Test statistic = 1.96, Degrees of freedom (for t) = 10, Test type = Two-tailed. Result: p-value: 0.049996; At the 5% level: Significant (p < 0.05); At the 1% level: Not significant (p ≥ 0.01).
Limits and caveats
- It works from the statistic alone, so make sure the test that produced it suits your data.
- A p-value does not measure effect size or the probability that the hypothesis is true.
Questions about this tool
When should I use a two-tailed test?
When a difference in either direction matters. Use one tail only if you fixed the direction before collecting data.
What are the degrees of freedom for a one-sample t-test?
The sample size minus 1. For two independent samples with equal variance it is n₁ + n₂ - 2.
What does p = 0.03 mean?
A result at least this extreme would appear 3% of the time if the null hypothesis were true, so it is significant at 5% but not at 1%.