Calculate a two-sided confidence interval for the difference between two independent conversion rates. Enter conversions and visitors for control and variant to see the observed absolute lift, relative lift, interval bounds, and a plain-language significance check.
The interval gives a range of differences compatible with the data under the normal approximation. If it excludes zero, the observed difference is statistically significant at the selected level.
For very small samples or conversion counts near zero, an exact or score-based interval may be more appropriate.
500/5,000 control conversions and 560/5,000 variant conversions produce rates of 10% and 11.2%. At 95% confidence, the difference is 1.2 percentage points with an interval of roughly −0.01 to 2.41 points.
It uses the inputs, formula, units, and independence assumptions shown on this page. Change the inputs to match your own system or experiment.
Use representative averages for planning, preserve headroom where applicable, and test multiple plausible scenarios instead of relying on one point estimate.
No. The result is a planning estimate. Validate it with measured data, monitoring, load tests, or an experiment-design review as appropriate.
The calculator checks values required by the formula and displays an error instead of returning NaN or Infinity. Valid zero values remain available where they are meaningful.
Tools may use different statistical approximations, unit conventions, rounding rules, priors, confidence definitions, or operational headroom assumptions.
| Variable | Unit | Meaning |
|---|---|---|
| p₁, p₂ | proportion | Observed conversions divided by visitors |
| SE | proportion | Unpooled standard error |
| CI | percentage points | Absolute difference interval |