Conversion rate uplift is the core metric of any A/B test. Two types matter: absolute uplift (variant rate − control rate, e.g., 4.1% − 3.2% = +0.9pp) and relative uplift ((variant − control) / control × 100, e.g., +28%). Relative uplift sounds more impressive but is harder to act on — a +20% relative lift on a 1% base is only 1.2%, while +20% on a 10% base is 12%. Always report both. Our calculator also computes the confidence interval around the uplift estimate, showing the range where the true effect likely lies.