P-value Calculator
Calculate the p-value for your statistical test. Supports z-test, t-test, chi-square test, and F-test. Choose the tail, enter the test statistic and degrees of freedom, and get the p-value plus a plain-language interpretation.
Full original guide (expanded)
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
—
Test statistic
—
df / parameters
—
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 testsp = 1 − F(x) for right-tailed testsp = F(x) for left-tailed tests
where F(x) is the CDF of Normal(0,1), t(df), χ²(df), or F(df₁, df₂).
Formula (LaTeX) + variables + units
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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
- PMI = private mortgage insurance (monthly) (currency)
- NIST — Weights and measures — nist.gov · Accessed 2026-01-19
https://www.nist.gov/pml/weights-and-measures - FTC — Consumer advice — consumer.ftc.gov · Accessed 2026-01-19
https://consumer.ftc.gov/
Last code update: 2026-01-19
- Initial audit spec draft generated from HTML extraction (review required).
- Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
- Confirm sources are authoritative and relevant to the calculator methodology.