Math Calculators
P-Value Calculator
Calculate p-values for z-scores and t-scores with precise tail test types.
What is the P-Value Calculator & How does it work?
The p-value is a measure of the probability that an observed result occurred by chance under the null hypothesis. Small values warrant rejection of the null hypothesis.
Two-Tailed: $p = 2 times (1 – Phi(|x|))$
$Phi(x)$ = Cumulative Distribution Function
$x$ = Absolute experimental test score ($Z$ or $t$)
$x$ = Absolute experimental test score ($Z$ or $t$)
Parameters
score
df
Computed P-value
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Frequently Asked Questions
What is a p-value?
A p-value measures the probability of observing your data (or something more extreme) if the null hypothesis is true.
How do I interpret a small p-value?
A small p-value (typically ≤ 0.05) indicates strong evidence against the null hypothesis, suggesting you should reject it.
What does a large p-value mean?
A large p-value (> 0.05) suggests weak evidence against the null hypothesis, so you fail to reject it.
How do I calculate a two-tailed p-value?
For a two-tailed test, multiply the one-tailed p-value by 2: $p = 2 imes (1 – Phi(|x|))$ where $Phi(x)$ is the cumulative distribution function and $x$ is your test score.
Can I use this calculator for both Z and t-scores?
Yes, you can input either a Z-score or a t-score into the calculator to find the corresponding p-value.
What is the null hypothesis in statistics?
The null hypothesis is a statement that there is no effect or no difference. It’s what you’re trying to test against with your data.
How do I know when to use a one-tailed vs two-tailed p-value?
Use a one-tailed test if you’re only interested in deviations in one direction from the null hypothesis. Use a two-tailed test if you’re interested in deviations in both directions.
Results are for informational purposes only and do not constitute professional advice.