%
% relative lift
visitors/day
The Verdict
Samples per variant
—
Total samples needed
—
Test duration
—
How this works (if you care)
This calculator uses the standard formula for determining sample size in a two-proportion z-test:
n = (Zα/2 + Zβ)² × [p₁(1-p₁) + p₂(1-p₂)] / (p₁ - p₂)²
Where:
- p₁ is your baseline conversion rate
- p₂ is the expected improved rate (baseline × MDE)
- Zα/2 is the z-score for your significance level
- Zβ is the z-score for your statistical power
For multiple variants, we apply a Bonferroni correction to maintain the overall significance level. The duration is calculated by dividing the total required samples by your daily traffic and rounding up to whole days.