Free A/B Testing Calculators
Statistical tools for people who run experiments: frequentist and Bayesian analysis side by side, sample size and power planning, and sequential testing — every result shareable as a link, with the math shown.
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Help me choose →A/B Test Calculator (Frequentist + Bayesian)
Frequentist and Bayesian analysis of your test, side by side
Open calculator →A/B Test Sample Size Calculator
How many visitors does your test need?
Open calculator →Statistical Power Calculator
What can your sample size actually detect?
Open calculator →MDE & Test Duration Calculator
What effect can you detect, and how long will it take?
Open calculator →Sequential Testing Calculator
Peek at results without inflating false positives
Open calculator →Learn the statistics
Guides
Statistical Significance in A/B Testing, Explained
What p-values, confidence levels, and significance actually mean in an A/B test — and the mistakes that make "significant" results wrong.
How to Size an A/B Test (Sample Size, MDE, and Power)
A practical walkthrough of sample size calculations: choosing an MDE, setting power, and translating the answer into test duration.
Bayesian vs Frequentist A/B Testing: Which Should You Use?
How Bayesian probability-to-be-best and expected loss compare to p-values and confidence intervals, and when each approach fits.
The Peeking Problem: Why Checking Results Early Breaks Your Test
Why repeatedly checking a fixed-horizon test inflates false positives, with simulations, and how sequential methods like mSPRT fix it.
Sample Ratio Mismatch (SRM): The Silent A/B Test Killer
How to detect sample ratio mismatch, the most common causes, and why you should throw away results from a test that fails an SRM check.