A/B Test Significance Calculator — Split-Test Z-Test

How to use

1. Enter visitors and conversions for variant A.
2. Enter visitors and conversions for variant B.
3. Press Evaluate to get rates, lift, z-score and p-value.
4. Read the 90/95/99% verdict chips before calling a winner.

General information only — not medical, financial or legal advice. Figures cross-checked against public official sources (IRS / HMRC / NHS / WHO guidance); content last reviewed September 2026. For decisions that matter, confirm with a licensed professional in your country.

About this tool

Two variants, four numbers — visitors and conversions for A and B — and this calculator does the statistics honestly: conversion rates, relative lift, the pooled two-proportion z-test with z-score and a two-tailed p-value computed by an embedded erf approximation, then verdict chips at the 90%, 95% and 99% confidence levels. It also refuses to flatter you: a minimum-sample guidance note warns that tiny tests produce big fake wins, and the assumptions behind the math — random split, independent visitors, binomial conversions — are stated rather than hidden. Product managers, marketers and indie founders can settle variant arguments in ten seconds, and because every number computes locally in your browser, your funnel data never leaves the page.

FAQ

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