A/B Test Calculator
Check A/B test significance — conversion lifts that are real vs noise. Stop shipping coin flips — free, local, no signup.
How to Use the A/B Test Calculator
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Frequently Asked Questions
Is my lift significant?
The tool runs a two-proportion z-test (pooled standard error) and calls significance at p < 0.05 with a 95% CI on the difference — no power analysis. Needs adequate volume: 100 conversions per variant minimum, more for small lifts. Peeking early inflates false positives. Three presets: Winner, Flat, Loser.
How long to run?
Full business cycles (1–2 weeks minimum) covering weekday/weekend variance. Stopping at significance courts regression to the mean.
What about segments?
Overall winners can lose in key segments — check mobile, new users, and top geos separately before full rollout.
Is test data uploaded?
No — math runs locally in your browser. Data never leaves your device.
Last updated October 2026