Our A/B test sample size calculator is powered by the formula behind our new Stats Engine, which uses a two-tailed sequential likelihood ratio test with false discovery rate controls to calculate statistical significance.
With this methodology, you no longer need to use the sample size calculator to ensure the validity of your results. Instead, the A/B test calculator is best used as a tool for planning out your testing program to find out how long you may need to wait before Optimizely can determine whether your results are significant, depending on the effect you want to observe.