Mann-Whitney U Test Calculator

Determine if there is a statistically significant difference between two independent groups without assuming your data is normally distributed. Enter your data below to instantly calculate the $U$-statistic, Z-score, and p-value.

How to use this calculator

1. Enter your data: Paste your raw data for Group 1 and Group 2 into the text boxes. Unlike an independent t-test, your groups do not need to be the same size, and your data does not need to follow a normal bell curve.
2. Set your parameters: Choose your significance level ($\alpha$) and whether you are running a one-tailed or two-tailed test. Two-tailed at an $\alpha = 0.05$ level is standard for most research.

Understanding Your Results

The Mann-Whitney U test (also known as the Wilcoxon rank-sum test) is the non-parametric alternative to the independent two-sample t-test. Instead of comparing the averages of the two groups, it compares their ranks.

• U-Statistic ($U$): The test calculates a $U$ score for both groups by checking how many times a value in Group 1 is smaller than a value in Group 2. The calculator outputs the smaller of the two $U$ values, which is the standard reporting metric.
• Z-Score: Because calculating exact probabilities for $U$ is mathematically heavy for large samples, the test converts the $U$ statistic into an approximate Z-score (a normal distribution metric). This calculator automatically applies a correction factor if there are “ties” (identical numbers) in your data.
• P-Value: The probability that a randomly selected value from Group 1 will be less than or greater than a randomly selected value from Group 2 purely by chance. If $p < \alpha$, the difference between your groups is statistically significant.