Enter a z-score (test statistic) to calculate the left-tail, right-tail, and two-tail p-values for hypothesis testing.
A p-value indicates the probability of observing a result as extreme as, or more extreme than, the actual result, assuming the null hypothesis is true.
P-values are derived from the standard normal cumulative distribution function applied to the z-score, for one-tail and two-tail hypothesis tests.
Enter your calculated z-score (test statistic) and click Calculate to see all three p-value variants.
Example: A z-score of 1.96 gives a two-tail p-value of approximately 0.05, the common threshold for statistical significance.
What is a typical significance threshold. Alpha equal to 0.05 is the most common threshold, meaning a p-value below 0.05 is considered statistically significant.
When should I use one-tail versus two-tail. Use a one-tail test when you only care about deviation in one direction, and two-tail when deviation in either direction matters.