Quick start
- Choose two-tailed, right-tailed, or left-tailed mode.
- Enter the z-score.
- Press Calculate p-value.
- Read the p-value and the left-tail and right-tail normal areas.
Best uses
Start here if one of these sounds like your job. The examples below show which inputs matter most.
- Estimate a p-value from a z-score in a statistics example.
- Compare left-tailed, right-tailed, and two-tailed test choices.
- See the left and right standard-normal tail areas.
- Check introductory hypothesis-testing work before writing an interpretation.
Choose the correct tail
Use a right-tailed test when unusually high values matter. Use a left-tailed test when unusually low values matter. Use a two-tailed test when a difference in either direction matters.
A two-tailed p-value doubles the smaller tail area because it counts extreme results on both sides of the normal curve.
What this calculator can and cannot do
This calculator uses the standard normal distribution. It is not a replacement for t tests, chi-square tests, ANOVA, exact tests, or software output that uses a different distribution.
A p-value helps describe how far into the comparison tail a result is. It does not prove a claim by itself, and it should be read with the study design, assumptions, and chosen significance level.
Worked examples for P-value Calculator
p is about 0.05
p is about 0.05
p is about 0.10
FAQ in plain language
What does this P-value Calculator use?
It estimates p-values from a z-score using the standard normal curve. It is for z-test style examples, not every statistical test.
Which tail should I choose?
Choose right-tailed when unusually high values matter, left-tailed when unusually low values matter, and two-tailed when differences in either direction matter.
What do the main P-value Calculator inputs mean?
The main inputs are the numbers, operation, mode, or known values the calculator needs. Keep units consistent, enter percentages the way the page label shows, and use the examples as a quick check before trusting the answer.
How should I read the P-value Calculator answer?
Read the headline answer, then check the supporting lines and examples to understand how the calculator got there. If one input changes, rerun the tool and compare the new answer instead of guessing.
What should I double-check before trusting the P-value Calculator?
Check units, signs, rounding, and the selected mode before copying the answer. If the number feels weird, rerun one of the examples first, then put your own values back in slowly.
What does a smaller p-value mean?
A smaller p-value means the observed z-score is farther into the tail of the comparison curve. It does not prove a claim by itself.
Is this the same as a t-test p-value?
No. A t-test uses a t distribution and degrees of freedom. This calculator uses the standard normal distribution from a z-score.
Sources
Use these if you want to compare the formula, inputs, or limits with a trusted outside explanation.
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Privacy and copying results
Recent answers stay visible only while you work in the current browser tab. They are not sent to a server.
Use Copy answer when you want to save the inputs and result in notes, homework, a message, or a project list. Check the units, labels, and limits before copying.