A/B Testing is the art of learning about your users with experiments: show half of them "A", show the other half "B", and measure the response in each group.

How many users do you need to run an A/B Test? If you have too few users in the experiment, you'll never see a difference between the two groups. If you have too many enrolled, the experiment will never end.

That's where A/B Buddy comes in: A/B Buddy helps you perform a statistically rigorous sample size calculation, with the slide of a finger, on your phone or on your iPad.

Let's say your current conversion rate is 10%, and you want to see if a proposed change from the design team can boost that number up to 12% -- that is, a 20% lift in the conversion rate. Simply pop open A/B Buddy, set the Baseline conversion rate to 10%, and the Minimum Detectable Effect to 20%, and your answer is waiting for you at the top of the screen.

A/B Buddy includes a Share button, which links to a web page displaying your sample size calculation. Your numbers, however, remain 100% private -- all the information is stored in the URL fragment, and is never transmitted to any servers.

By default, A/B Buddy uses the most common statistical thresholds: 5% for the significance level (false-positive rate), and 80% for the power level (ability to detect the Minimum Detectable Effect). Power users can adjust these values after unlocking the Pro Features in-app purchase. But most users will find the defaults adequate for their needs.

Questions? Suggestions? Ideas? Feedback is always welcome at


Evan Miller
8.8 MB
Requires iOS 10.0 or later. Compatible with iPhone 5s, iPhone 6, iPhone 6 Plus, iPhone 6s, iPhone 6s Plus, iPhone SE, iPhone 7, iPhone 7 Plus, iPhone 8, iPhone 8 Plus, iPhone X, iPhone XS, iPhone XS Max, iPhone XR, iPad Air, iPad Air Wi-Fi + Cellular, iPad mini 2, iPad mini 2 Wi-Fi + Cellular, iPad Air 2, iPad Air 2 Wi-Fi + Cellular, iPad mini 3, iPad mini 3 Wi-Fi + Cellular, iPad mini 4, iPad mini 4 Wi-Fi + Cellular, 12.9-inch iPad Pro, 12.9-inch iPad Pro Wi-Fi + Cellular, 9.7-inch iPad Pro, 9.7-inch iPad Pro Wi-Fi + Cellular, iPad (5th generation), iPad Wi-Fi + Cellular (5th generation), 12.9-inch iPad Pro (2nd generation), 12.9-inch iPad Pro Wi‑Fi + Cellular (2nd generation), 10.5-inch iPad Pro, 10.5-inch iPad Pro Wi‑Fi + Cellular, iPad (6th generation), iPad Wi-Fi + Cellular (6th generation), iPad Pro (11-inch), iPad Pro (11-inch), iPad Pro (12.9-inch) (3rd generation), iPad Pro (12.9-inch) (3rd generation), and iPod touch.
Age Rating
Rated 4+
© 2019 Evan Miller
In-App Purchases
  1. Pro Features $8.99


  • Family Sharing

    With Family Sharing set up, up to six family members can use this app.

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