A/B Test Significance Calculator

Free tool · Testing

Is your test a winner, or just noise?

Paste your visitors and conversions for both variants. Get the conversion rates, uplift and a proper two-tailed significance check before you roll anything out.

Your numbers

Variant A (control)

Variant B (challenger)

Results

Conversion rate A
Conversion rate B
Relative uplift
Confidence
Enter your test data and check.

How it works

This runs a standard two-proportion z-test (two-tailed). At 95%+ confidence the difference is very unlikely to be random luck; below 90% you genuinely don’t know yet.

Three rules I hold clients to: decide the sample size before the test, never peek-and-stop the moment it flips green, and run at least one full business cycle (7 days minimum) so weekday and weekend behaviour are both in the data.

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