A/B Test Significance Calculator

Find out whether your A/B test result is real or just noise. Enter visitors and conversions for each variant and this free A/B test calculator runs a two-proportion z-test to give you both conversion rates, the relative uplift, a p-value and a plain-language verdict at 90%, 95% or 99% confidence. Built for marketers, CRO specialists and product teams — everything is calculated in your browser.

Your result will appear here

Enter visitors and conversions for both variants to see the winner and its statistical significance.

How to use

Enter the visitors and conversions for Variant A (your control).
Enter the visitors and conversions for Variant B (your variation).
Pick your confidence level — 95% is the standard for most tests.
Read the verdict: conversion rates, relative uplift, p-value and whether the result is significant update instantly.
Click "Copy result" to paste the full summary into a report or chat.

Features

Two-proportion z-test with two-tailed p-value — the standard method for comparing conversion rates
Conversion rate for each variant with a side-by-side bar comparison
Relative uplift showing how much better (or worse) B performs versus A
Plain-language verdict and a coloured significance badge at 90 / 95 / 99% confidence
Small-sample guard that warns you when there is too little data to trust the result
100% in-browser — your test data never leaves your device

Frequently asked questions

What does statistical significance mean in an A/B test?

It tells you how likely the difference between two variants is real rather than random chance. A result "significant at 95%" means there is a 5% or smaller probability the observed difference happened by luck, so you can trust the winner.

What is a p-value and how do I read it?

The p-value is the probability of seeing a difference this large if the two variants were actually identical. Lower is stronger. If your p-value is below your significance threshold (0.05 for 95% confidence), the result is statistically significant.

Why does it warn me about small sample sizes?

When fewer than about 5 conversions are expected in any group, the z-test approximation becomes unreliable and can flag a "winner" that is really noise. The tool hides the verdict and asks you to gather more data before drawing conclusions.

Which statistical test does this calculator use?

It uses a pooled two-proportion z-test with a two-tailed p-value, computed from an error-function approximation. This is the standard frequentist method for comparing two conversion rates and matches what most A/B testing platforms report.

Is my test data sent to a server?

No. Every calculation runs in JavaScript in your browser — nothing is uploaded or stored. You can even use the tool offline once the page has loaded.

A/B Test Significance Calculator

Variant A (control)

Variant B (variation)

How to use

Features

Frequently asked questions

A/B Test Significance Calculator

Variant A (control)

Variant B (variation)

How to use

Features

Frequently asked questions

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