Tool
Incrementality Calculator
Plug in your test and control group results to measure incremental lift, incremental CAC, and statistical significance, instantly.
New to incrementality? Read the incrementality definition
Your numbers
Rule of thumb: if incremental CAC is dramatically higher than your platform-reported CAC, the channel is over-credited and likely needs a budget cut.
How to Calculate Incremental Lift
Incrementality testing isolates the conversions your ads caused from the conversions that would have happened anyway. You hold out a matched control group from all advertising, then compare results.
Incremental Conversions = Test Conversions − Control Conversions Lift % = (Test − Control) ÷ Control Incremental CAC = (Test Spend − Control Spend) ÷ Incremental Conversions Example: Test: 520 conv from $8,000 spend Control: 410 conv from $0 spend Incremental = 520 − 410 = 110 conversions Lift % = 110 / 410 = +26.8% iCAC = $8,000 / 110 = $72.73
When to Run an Incrementality Test
- Scaling budgets beyond $50k/mosmall reporting errors become big dollar leaks.
- Launching new offline or top-of-funnel channels where click attribution doesn't apply.
- When platform CPA drastically disconnects from backend CAC.
What is an incrementality test?
An incrementality test (also called a lift study or geo-holdout) measures the true causal impact of advertising by comparing a group exposed to ads (test) with a matched group that was not (control). The difference between the two is the incremental conversions your ads actually caused, separating real ad-driven sales from sales that would have happened anyway.
How do you calculate incremental lift?
Incremental Lift % = (Test Conversion Rate − Control Conversion Rate) ÷ Control Conversion Rate. Incremental Conversions = Test Conversions − (Control Rate × Test Population). Incremental CAC = Test Spend ÷ Incremental Conversions.
When is a lift test statistically significant?
At a 95% confidence level, a two-proportion z-test result with |z| ≥ 1.96 is considered significant. If your sample sizes are small or the lift is marginal, you usually need more traffic or a longer test window.
When should you run an incrementality test?
Run incrementality tests on always-on channels (branded search, retargeting, Performance Max, broad prospecting on Meta) where platform-reported ROAS overstates true contribution. They are especially valuable post-iOS 14 as click-based attribution has become noisier.
Not sure if your ads are actually driving growth?
Book a free growth gap audit, we'll design a geo-lift or holdout test that gives you a defensible answer.
Email me this lift result
Send me your test and control numbers and I'll come back with a short note on whether the lift is real and what to do next.