Enter the visitors and conversions for each version. You get each conversion rate, the lift, and whether the difference is statistically significant or could still be chance.

Version A (control)

Version B (variant)

Confidence level
A
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B
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Lift (B vs A)
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Confidence the difference is real
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Reading the result

The test compares the two conversion rates (a two-sided two-proportion z-test). "Significant at 95%" means a difference this big would happen by chance less than 5% of the time. Run tests for full weeks and decide the sample size up front - stopping the moment a result looks good makes false wins likely.