Instructions: Enter parameters in the red cells. Answer will appear in blue below.

α (two-tailed) = Threshold probability for rejecting the null hypothesis. Type I error rate.
β = Probability of failing to reject the null hypothesis under the alternative hypothesis. Type II error rate.
P0 = Proportion in Group 0 (baseline proportion)
N1 = Number of subjects in Group 1
N0 = Number of subjects in Group 0
P1 is expected to be greater than
less than
the value of P0.

This study has 80.0% power to detect a P1 =

Follow this link to see the formula used in this calculator.


Fleiss, JL, et al. Statistical methods for rates and proportions. Hoboken, NJ, J. Wiley; 2003. Page 79.