A/B Test Calculator

Plan how long to run your test, check if the result is real, and find out whether you can stop. Your numbers never leave this page.

Your test setup

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What do confidence and power mean?

Confidence: how sure you want to be that a winner is real and not luck. At 95%, about 1 in 20 "winners" in tests with no real difference would be false alarms.

Power: the chance your test spots a lift if it really exists at the size you entered. At 80%, a real lift of that size is missed about 1 time in 5.

What you need

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In plain English