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A/B Test Significance Calculator

Compare two variants and see whether the difference is conclusive.

Marketing Tools Reviews Free · no sign-up

Variant A is the control, variant B the challenger. Use the same date range for both.

Relative uplift, B vs A

—

Variant A rate—
Variant B rate—
Absolute difference—
Confidence level—

Quick Tool Overview

The A/B Test Significance Calculator compares two variants by visitors and conversions, working out both conversion rates, the relative uplift and the confidence level from a two-tailed z-test, then says plainly whether the result is conclusive.

What it does
Tests whether a difference between two variants is significant
You give it
Visitors and conversions for variant A and variant B
You get back
Both conversion rates, uplift, confidence level, and a verdict
Best for
Deciding whether a split test result is safe to ship
Marketing Tools Free, unlimited use No sign-up Runs in your browser

About the A/B Test Significance Calculator

The hardest part of an A/B test is not running it — it is resisting the urge to call a winner too early. A variant three points ahead after 200 visitors usually means nothing at all, and shipping on that basis is how teams end up chasing noise for months.

Enter visitors and conversions for both variants and the calculator works out each conversion rate, the relative uplift, the absolute difference in percentage points, and the confidence level from a two-tailed z-test of two proportions. The verdict underneath says plainly whether the result clears the usual 95% threshold, is leaning that way, or could still easily be chance — with a warning when the sample is too small to trust either way.

Key features of the A/B Test Significance Calculator

Proper statistics

A two-tailed z-test for two proportions, not a rule of thumb.

Plain-English verdict

Says whether the result is conclusive, leaning, or still noise.

Small-sample warning

Flags when there are too few conversions to trust the answer either way.

Runs in your browser

No sign-up, no data sent anywhere.

How to use the A/B Test Significance Calculator

  1. 1

    Enter variant A

    Visitors and conversions for the control.

  2. 2

    Enter variant B

    Visitors and conversions for the challenger.

  3. 3

    Read the uplift

    Both conversion rates, the relative uplift and the absolute difference.

  4. 4

    Check the verdict

    Confidence level plus a plain-English read on whether the result is conclusive.

Frequently asked questions

This calculator uses a two-tailed z-test for two proportions: z = (rate B − rate A) ÷ the square root of pooled rate × (1 − pooled rate) × (1 ÷ visitors A + 1 ÷ visitors B), where the pooled rate is total conversions divided by total visitors. The confidence level is 100% minus the resulting p-value.

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