P-value Calculator
Calculate p-value from z-score or t-statistic for one-tailed and two-tailed hypothesis tests. Determine if results are statistically significant. Free.
P-value Calculator
toolznova.com • Free Calculator
How to Use
Calculate p-value in 3 steps.
Choose Test Type
Select Z-test or T-test, and one-tailed or two-tailed.
Enter Test Statistic
Enter your Z-score or T-statistic (and df for t-test).
Get P-value
Click Calculate for p-value, significance, and decision.
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Why Calculate P-value?
- Hypothesis Testing: P-value is the core of statistical hypothesis testing.
- Research: Medical, social, and scientific studies require p-values.
- A/B Testing: Determine if differences in tests are statistically significant.
- Quality Control: Test if process metrics differ from target values.
- Regression: P-values test significance of regression coefficients.
- ANOVA: Testing differences between group means uses F-tests and p-values.
Tips & Examples
- P-value is the probability of observing results as extreme as yours IF H₀ is true.
- P < 0.05 is the conventional threshold for statistical significance.
- Smaller p-value = stronger evidence against the null hypothesis.
- P < 0.001: very strong evidence. P < 0.05: moderate. P > 0.10: weak.
- Two-tailed test: appropriate when you test for any difference (not just one direction).
- One-tailed test: when you predict direction of difference before collecting data.
Free P-value Calculator Online
ToolzNova's free p-value calculator computes p-values for Z-tests and T-tests (one-tailed and two-tailed), compares to significance level α, and gives a clear reject/fail-to-reject decision for hypothesis testing.
The p-value is the probability of observing your test result (or more extreme) if the null hypothesis were true. A p-value below the significance threshold (α, typically 0.05) is evidence to reject the null hypothesis.
P-value and Hypothesis Testing
One-tailed right: p = P(Z > z). One-tailed left: p = P(Z < z). Two-tailed: p = 2×P(Z > |z|). Decision: if p < α, reject H₀. If p ≥ α, fail to reject H₀.