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
These are the situations this tool is meant for. If your task is close to one of these, the examples and notes below can help you choose the right inputs.
- 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.
Examples from the 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 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.
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- Z-score Calculator Calculate a z-score and approximate standard normal percentile.
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- Confidence Interval Calculator Calculate z confidence intervals for a mean or a proportion.
Privacy and copying results
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Use Copy answer when you want to paste the expression and result into notes, homework, a message, or another document. Check the units and assumptions before copying.