Estimate the probability that a two-sided A/B conversion test will detect the specified lift at a chosen sample size. Use it to check whether an existing traffic plan is sufficiently sensitive before launching or interpreting a fixed-horizon experiment.
The critical threshold uses the pooled null standard error; power is evaluated under the entered alternative.
Power is the chance of rejecting the equal-rate null when the entered conversion rates are the true rates.
The approximation assumes independent users, equal group sizes, one final analysis, and a binary outcome.
With 15,000 users per variant, rates of 10% and 11%, and 95% confidence, estimated power is about 81%.
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 |
|---|---|---|
| Δ | percentage points | Variant rate minus baseline |
| SE₁ | proportion | Standard error under the alternative |
| Power | probability | Detection probability if the effect is real |