z or t P-Value Calculator

Statistics

z or t P-Value with explicit assumptions and reproducible inputs.

Formula

For two-sided tests p=2P(T≥|statistic|); choose left or right tail for directional alternatives.

Use the units shown beside each field.
Results update automatically whenever you change an input.
Displayed values use up to four decimal places, or scientific notation for very small or large numbers. Calculations use standard floating-point arithmetic; exact integer and fraction tools identify their own precision rules.
The reference distribution and test statistic must be justified by the study design. A p-value is not the probability that the null hypothesis is true. Numerical results are approximate. Extremely small probabilities can underflow to zero. No personal, clinical or financial decision rule is inferred.

Example Calculation

Example inputs

Reference distribution: Standard normal (z)
Test statistic: 1.96
Degrees of freedom (t only): 24
Alternative: Two-sided

A two-sided z test with statistic 1.96 gives p≈0.049996.

Method references

itl.nist.gov — method reference

Frequently asked questions

How do I use this calculator?

Enter reference distribution, test statistic, degrees of freedom (t only), alternative. The result updates automatically. Use Reset to restore the example values.

What method does it use?

For two-sided tests p=2P(T≥|statistic|); choose left or right tail for directional alternatives.. The reference distribution and test statistic must be justified by the study design. A p-value is not the probability that the null hypothesis is true. Numerical results are approximate. Extremely small probabilities can underflow to zero. No personal, clinical or financial decision rule is inferred.

Why might a rounded result differ?

The calculation keeps full numeric precision internally, then rounds the displayed result. Rounding intermediate steps by hand can produce a slightly different answer.

Are my inputs saved online?

No. This calculator processes your inputs in your browser. A recently used list stores only calculator names on this device, not your entered values.

Check the assumptions and units before using this result. Read about calculation methods.