Free
A/B Test
Calculator
The A/B Test Calculator helps you plan and analyze experiments with precision. It calculates sample size, test duration, and statistical significance, ensuring your A/B tests are backed by solid data for confident decision-making.
Pre-Test Calculator – MDE
- What is the minimum detectable effect (MDE) to consider?
- How long should the test run to detect meaningful results?
- What’s the sample size required for this test?
- How does the confidence level influence the test duration?
How to Use?
This section helps you estimate the required sample size for a valid experiment and the time needed to run your A/B test.
- Input your data:
- Confidence Level: Keep it at 95% for industry-standard confidence.
- Statistical Power: 80% is commonly used, but you can adjust.
- Conversion rate for control: Enter the current conversion rate of your control group (e.g., 10%).
- Number of variants: Specify how many test variants you are comparing against the control.
- Weekly Conversions: The number of conversions you typically get in a week. Used to get an estimate of how many weeks you need to run your experiment.
- Calculate your MDE:
Click Calculate to find out:- Minimum Detectable Effect (MDE): The smallest effect size you aim to detect in a study.
- Significance: Represents a meaningful difference you don’t want to miss if it exists.
- Expression: Entered as a percentage, either relative or absolute.
- Relation to Control: MDE is either relative to or an absolute difference from the control conversion rate.
- Example:
- Control conversion rate = 10%
- Desired minimum test variant conversion rate = 15%
- MDE absolute = 5% – (15 – 10)
- MDE relative = 50% – (15 – 10) / 10 × 100
Data Input
Results
| Sample Size per Group: | |
| Total Sample Size: | |
| Estimated Duration (weeks): |
Test Result Calculator
Once you’ve collected all your data, you can test if your variant is significantly different from the control. Before using this calculator, ensure the following:
- Required Sample Size: The test has reached the necessary sample size.
- Avoid Multiple Testing: Test only once you have collected all your data. Testing multiple times increases the risk of Type I errors by inflating the chance of finding a significant result by chance. Stick to your planned sample size and test duration before analyzing.
How to Use?
This section helps you analyze the performance of your A/B test to determine if your results are statistically significant.
- Input the following data:
- Control Visitors: Enter the total number of visitors who saw the control version of the experiment.
- Control Conversions: Enter the number of conversions (e.g., purchases, sign-ups) from those who saw the control version.
- Variant Visitors: Enter the total number of visitors who saw the test variant.
- Variant Conversions: Enter the number of conversions from those who saw the test variant.
- Confidence Level (%): Keep it at 95% (industry standard) or adjust if needed.
- Click “Calculate” to view the results:
The results will display important metrics, including the conversion rates, lift, confidence interval of the difference between, p-value, z-score, and whether the results are statistically significant. We suggest looking at the 1-sided tests since they are more relevant for A/B testing.
Data Input
Results
| Control Conversion Rate | – |
| Variant Conversion Rate | – |
| Lift (%) | – |
| Absolute differences | |
| Absolute difference | – |
| Confidence Interval (Difference, %) | – |
| Right-Sided Interval (%) | – |
| Left-Sided Interval (%) | – |
| Value ± SE (%) | – |
| P-Value (One-sided) | – |
| P-value (Two-sided) | – |
| Z-Score | – |
| Significance (One-sided) | – |
| Bayesian Probability: Variant Wins (%) | – |
| Bayesian Probability: Control Wins (%) | – |
| Bayes Factor (H1/H0) | – |
| Relative differences | |
| Relative Confidence Interval (Difference, %) | – |
| Relative Right-Sided Interval (%) | – |
| Relative Left-Sided Interval (%) | – |
| Relative Difference ± SE | – |
| Relative P-Value | – |
| Relative Z-Score | – |
Become
Certified
at CRO
Become a certified expert at conversion optimization with this
comprehensive online course.
- Learn how to build and run world-class optimization programs
- Master everything there is to master about A/B testing
- Immediately apply learnings with hundreds of playbooks
- Drive better results without increasing costs
Marketers choose CXL
Get scale-up growth strategies in your inbox.
An expert-led newsletter focused on helping marketing teams at growth/expansion stage companies
overcome growth challenges, crush their competition, and stand out in the market.
Join 140,000+ marketers | Subscribe to our educational newsletter