A/B test planning — sample size, MDE and duration
Enter baseline conversion, expected uplift, power, confidence and daily traffic.
Planned and detectable effect
| Scenario | Baseline | Target | n per variant |
|---|---|---|---|
| Fill in the fields above — the result is computed on this page. | |||
How do I use this page?
- Enter baseline conversion from 0 to 1.
- Set the smallest relative effect that matters.
- Review sample size, MDE and duration, then set a complete schedule.
What this page does not do: The formula uses a normal approximation, equal allocation and independent users. It does not account for repeated peeking, clustering or multiple metrics.
Further reading
Theory — how is sample size planned for an A/B test?
The plan calculates the number of observations needed to compare two independent proportions with a two-sided test, based on baseline conversion, expected uplift, statistical power, confidence level and daily traffic. The MDE value shows the smallest relative uplift that the given available sample can detect at the chosen power. Test duration is calculated by dividing the total required sample by daily traffic. Conversion rates and relative uplift are entered as fractions, so 0.1 means 10 percent.
Frequently asked questions
Does 0.1 mean 10%?
Can I stop the test early?
See also
A/B test calculator
Compare two proportions in an A/B test. Calculate conversion rates, difference, uplift, z score, p value and c
ACF and PACF autocorrelation calculator
Calculate ACF and PACF across time-series lags. Review the chart, reference bounds and coefficient table.
Adjusted R-squared calculator
Convert R² to adjusted R² using the number of observations and predictors in a regression model.