What confidence level should I use for my A/B test?

Most marketers use 95% as the standard, but if you want stronger evidence, 99% reduces the chance of a false positive at the cost of needing larger sample sizes.

How large does my sample size need to be?

Sample size depends on your current conversion rate and the minimum lift you want to detect; higher baseline rates or smaller desired lifts require more visitors to achieve statistical significance.

What does a p-value below 0.05 mean in an A/B test?

It means there is less than a 5% probability that the observed difference is due to random chance, so you can reject the null hypothesis and claim a statistically significant result.

Can I use a one-tailed test instead of two-tailed?

Use a one-tailed test only if you decided in advance that you only care about one variant beating the other; otherwise, stick with two-tailed to avoid inflating your significance chances.

Why do some calculators show lift as a percentage and others as percentage points?

Percentage points measure the absolute difference between two rates, while relative lift expresses that difference as a proportion of the original rate; both are useful depending on whether you want to emphasize size or proportional change.

Statistics2 options compared

AB Test Calculator

Calculates the statistical significance of A/B tests by inputting sample sizes, conversion rates, and desired confidence levels. Offers quick, reliable results to help users determine if changes are statistically significant. Ideal for marketers, web developers, and anyone conducting A/B testing to improve website or product performance.

Inference, regression, and statistical tests calculators

Editors’ Top PickBased on community votes

Omni Calculator

omnicalculator.com

Determine the statistical significance of your A/B tests effortlessly with our AB test calculator. Reliable, quick re...

Open Omni Calculator Read review →

Other OptionsRanked by votes

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TrafficLoopback
trafficloopback.com
A/B test significance calculator that returns the p-value, z-statistic, observed lift, and confidence interval from a...
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Side by side

AB Test Calculator options compared

Tool	Best for	Strengths	Limitations
Omni Calculator omnicalculator.com	Quick significance checks	Community-vetted design Simple confidence level selectors	Fewer statistical outputs No plain-English verdict
TrafficLoopback trafficloopback.com	Detailed test outputs	P-value and z-statistic Confidence intervals and lift percentages	Zero community votes More data points to parse

Buyer's guide

How to choose a ab test calculator

When picking an A/B test calculator, decide whether you need only a yes/no significance result or a full statistical breakdown. If you just want to know if a change matters, a tool with clear confidence level buttons is fastest. If you need to report lift percentages, p-values, or confidence intervals to stakeholders, choose one that outputs those details directly.

Questions

AB Test Calculator FAQ

What confidence level should I use for my A/B test?: Most marketers use 95% as the standard, but if you want stronger evidence, 99% reduces the chance of a false positive at the cost of needing larger sample sizes.
How large does my sample size need to be?: Sample size depends on your current conversion rate and the minimum lift you want to detect; higher baseline rates or smaller desired lifts require more visitors to achieve statistical significance.
What does a p-value below 0.05 mean in an A/B test?: It means there is less than a 5% probability that the observed difference is due to random chance, so you can reject the null hypothesis and claim a statistically significant result.
Can I use a one-tailed test instead of two-tailed?: Use a one-tailed test only if you decided in advance that you only care about one variant beating the other; otherwise, stick with two-tailed to avoid inflating your significance chances.
Why do some calculators show lift as a percentage and others as percentage points?: Percentage points measure the absolute difference between two rates, while relative lift expresses that difference as a proportion of the original rate; both are useful depending on whether you want to emphasize size or proportional change.

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