Two-tailed z test
z = 1.96p is about 0.05
P-value Calculator
Use this free p-value calculator to estimate a normal-curve p-value from a z-score, choose left-tailed, right-tailed, or two-tailed mode, and see the tail areas.
Inputs to check Example numbers Copyable answer Tab-only history
Two-tailedp = 0.0499956522
- Left tail
- 0.9750021739
- Right tail
- 0.0249978261
- Z-score
- 1.96
Steps
- Use the standard normal curve where mean is 0 and standard deviation is 1.
- Find the left-tail area for z = 1.96.
- Double the smaller tail area for a two-tailed p-value.
- The p-value is 0.0499956522.
How to use the P-value Calculator
- Choose left-tailed, right-tailed, or two-tailed mode.
- Enter the z-score from your statistics problem.
- Press Calculate p-value to see the standard-normal tail areas.
- Use the result as a quick normal-curve estimate, then check whether your assignment needs a different distribution.
What people use it for
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.
Quick examples
Right-tailed example
z = 1.645p is about 0.05
Left-tailed example
z = -1.28p is about 0.10
Need the guide or a nearby tool?
Need a slower walkthrough, a related calculator, or the full library? These links keep you close to the task you started.
- How to use the P-value Calculator See slower examples, input meanings, formula notes, result limits, and mistakes to avoid.
- Calculators Browse related calculators and utilities in the same category.
- Calculator and utility guides Find more guides that use real tool inputs and example numbers.
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Frequently asked questions
Quick answers about formulas, inputs, examples, result copying, and private in-browser history.
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.
Why is the two-tailed value doubled?
A two-tailed test counts extreme results in both directions, so it doubles the smaller tail area while keeping the result no higher than 1.
Is my z-score history private?
Yes. Recent answers stay only in your current browser tab and are not sent to a server.