Rex says
The fast lane for the math you almost remember from school. Type the numbers, get the answer, move on with your day.
Try a scenario
Click to load — tweak from there.Inputs
Result
Verdict
Significant at 95% (p = 0.0163)
Relative lift
22.00%
Control conversion rate
5.000%
Variant conversion rate
6.100%
Confidence level
98.37%
Z-statistic
2.4022
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
How to use this
- 1Enter control visitors.
- 2Enter control conversions.
- 3Enter variant visitors.
- 4Enter variant conversions.
- 5Read your verdict on the right — it updates as you type.
- 6Hit Share to keep the scenario or send it to someone.
About this calculator
Runs a two-proportion z-test on your control and variant. Stopping a test the moment it looks good is how teams ship changes that do nothing — wait for significance and a pre-planned sample size.
Worked example
Using the values the calculator loads with:
Inputs
- Control visitors: 5000
- Control conversions: 250
- Variant visitors: 5000
- Variant conversions: 305
Results
- Verdict: Significant at 95% (p = 0.0163)
- Relative lift: 22.00%
- Control conversion rate: 5.000%
- Variant conversion rate: 6.100%
- Confidence level: 98.37%
- Z-statistic: 2.4022
What each field means
Inputs
- Control visitors
- The control visitors used in the calculation. Starts at 5000 so you have a working example on load.
- Control conversions
- The control conversions used in the calculation. Starts at 250 so you have a working example on load.
- Variant visitors
- The variant visitors used in the calculation. Starts at 5000 so you have a working example on load.
- Variant conversions
- The variant conversions used in the calculation. Starts at 305 so you have a working example on load.
Results
- Verdict
- Returned as a plain value and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Relative lift
- Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Control conversion rate
- Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Variant conversion rate
- Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Confidence level
- Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Z-statistic
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the a/b test significance calculator work?
Runs a two-proportion z-test on your control and variant. Stopping a test the moment it looks good is how teams ship changes that do nothing — wait for significance and a pre-planned sample size. The underlying maths is: z = (p₂ − p₁) ÷ √(p(1−p)(1/n₁ + 1/n₂)) using the pooled conversion rate.
What do I need to enter?
4 values: control visitors, control conversions, variant visitors, and variant conversions. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the verdict result mean?
It is returned as a plain value and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Results are rounded for display; the underlying calculation keeps full precision.
Who is this tool for?
It's built for students, developers, and anyone who needs the answer right now without setting up a spreadsheet.
Accuracy and limitations
- Results are rounded for display; the underlying calculation keeps full precision.
- Very large or very small inputs may hit floating-point limits in the browser.
- Inputs outside the accepted range are clamped rather than rejected.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). A/B Test Significance Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/ab-test
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/ab-test" target="_blank" rel="noopener">A/B Test Significance Calculator — RevenueLab</a> (2026).</p>
Source: [A/B Test Significance Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/ab-test) (2026).