How to use the P-value Calculator
The p-value calculator converts a z-score to a p-value for a one- or two-tailed test.
What you need to enter
- Z-score
- Test type
The formula
Two-tailed p = 2 × (1 − Φ(|z|)), where Φ is the normal cumulative distribution.
Worked example
Using the default values in the calculator:
- Z-score: 1.96
- Test type: Two-tailed
| P-value | 0.049996 |
| Significant at 0.05? | Yes |
| Significant at 0.01? | No |
Tips for better results
- Choose the tail before looking at data.
- p below 0.05 is a common threshold.
Common mistakes to avoid
- Calling p the probability the hypothesis is true.
- p-hacking.