P-value Calculator

Enter your test statistic, pick the distribution, and instantly see the p-value. Works for z, t, chi-square, and F.

1. Test input

For t: use df. For chi-square: df. For F: numerator df.

2. Calculate

3. Output

p-value

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Test statistic

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df / parameters

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What is a p-value?

A p-value tells you how extreme your test statistic is under the null hypothesis. It does not tell you the probability that the null hypothesis is true. Very small p-values indicate your data would be rare if the null hypothesis were correct.

Common thresholds

  • p < 0.10 → weak evidence
  • p < 0.05 → standard level of significance
  • p < 0.01 → strong evidence against H₀

Formulas used

We use the CDF of the selected distribution:

p = 2 × min(F(x), 1 − F(x)) for two-tailed tests
p = 1 − F(x) for right-tailed tests
p = F(x) for left-tailed tests

where F(x) is the CDF of Normal(0,1), t(df), χ²(df), or F(df₁, df₂).