Incremental lift equals the conversion rate of the exposed group minus the conversion rate of the control group, divided by the control group's rate. If 2.4 percent of exposed users converted and 2.0 percent of a randomized holdout did, lift is 20 percent and incremental conversions are 0.4 percent of the exposed group. Incremental CPA equals spend divided by those incremental conversions.
What moves it
The groups must be randomized before exposure, the test must be sized in advance to detect the expected lift, and the result carries a confidence interval that should be reported with it. Geo tests replace user groups with markets and use the same arithmetic.
Run your own numbers with the Lift test sample size calculator.
Cite this page:
Agency Echelon. "How do you calculate incremental lift?" Agency Echelon Reference, reviewed September 2026. https://agencyechelon.com/reference/questions/how-to-calculate-incremental-lift/