Free P-Value Calculator Online
This free online p-value calculator computes p-values from z-scores or t-statistics for one-tailed and two-tailed hypothesis tests.
Test Parameters
P-Value
Enter test statistic above
How the P-Value Calculator Works
The p-value calculator takes your test statistic (z-score or t-statistic), the type of test (one-tailed or two-tailed), and optional degrees of freedom for t-tests. It then computes the p-value using the cumulative distribution function. The p-value calculator shows whether the result is statistically significant at common thresholds.
For a z-score of 2.0 with a two-tailed test, the p-value calculator gives p = 0.0455 — significant at the 0.05 level but not at 0.01. A z-score of 2.576 gives p ≈ 0.01 (two-tailed), the threshold for 99% confidence. The p-value calculator makes these lookups instant.
The p-value calculator also computes t-distribution p-values when you specify degrees of freedom. T-distributions have heavier tails than the normal distribution, so the same test statistic yields a larger p-value for small sample sizes. The p-value calculator accounts for this difference.
Interpreting P-Values
A small p-value (typically ≤ 0.05) provides evidence against the null hypothesis. It does NOT prove the alternative hypothesis is true — it indicates the observed data would be unlikely under the null. The p-value calculator quantifies this evidence.
Common significance levels: 0.10 (weak evidence), 0.05 (moderate), 0.01 (strong), 0.001 (very strong). The p-value calculator tells you which thresholds your result passes. Always report the exact p-value from the p-value calculator, not just "significant" or "not significant."
The p-value calculator is a tool for hypothesis testing in research, A/B testing, clinical trials, and quality control. Combine p-values with effect sizes and confidence intervals for a complete statistical picture.
Tips for Using the P-Value Calculator
Choose the Right Tail
Use two-tailed for "different from" hypotheses, one-tailed for "greater than" or "less than." The p-value calculator supports both.
Z vs T
Use z-score for large samples (n≥30). Use t-statistic with degrees of freedom for small samples. The p-value calculator handles both.
Report Exact P
Always report the exact p-value from the p-value calculator rather than just "p < 0.05." This gives readers more information.
Significance ≠ Importance
A small p-value means statistically significant but not necessarily practically important. Consider effect size alongside the p-value calculator result.
Frequently Asked Questions
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