Definition
Incrementality estimates the conversions that would not have happened without ads (true lift).
Example
If the exposed group converts at 5.0% and the holdout group converts at 4.6%, incremental lift is 0.4 percentage points (about 8.7% relative lift).
How to use it
- Use holdouts or geo-experiments to estimate incremental lift.
- Be careful with short tests when purchase cycles are long.
Common mistakes
- Treating attribution as causal truth (it's model-based credit).
- Running tests without clean holdouts (contamination breaks results).
Why this matters
This term matters because it affects how you interpret performance and make budget decisions. If you use inconsistent definitions or windows, ROAS/CPA can look "better" while profit gets worse.
Practical checklist
- Write a 1-line definition for "Incrementality" that your team will use consistently.
- Keep the time window consistent (weekly/monthly/quarterly) when comparing trends.
- Segment results (channel/plan/cohort) before drawing big conclusions from blended averages.
- Use a calculator that references this term (e.g., Incrementality Lift Calculator) to sanity-check assumptions.
- Read the related guide (e.g., Incrementality: how to tell if ads are actually driving growth) for context and common pitfalls.
Where to use this on MetricKit
Calculators
- Incrementality Lift Calculator: Estimate incremental conversions, incremental ROAS, and incremental profit from a holdout test.
- Marginal ROAS Calculator: Estimate diminishing returns and find the profit-maximizing ad spend from a simple response curve.
- Target CPA from LTV Calculator: Translate LTV and contribution margin into a target CPA (and break-even CPA) for paid acquisition.
- MER Calculator: Calculate MER (Marketing Efficiency Ratio / blended ROAS) and estimate break-even and target MER from margin assumptions.
Guides
- Incrementality: how to tell if ads are actually driving growth: Platform-reported ROAS can overstate impact. Learn what incrementality means, when it matters, and practical ways to test it.
- Incrementality lift: how to compute incremental ROAS from holdouts: Turn an exposed vs holdout test into incremental conversions, incremental ROAS, and incremental profit for decision-making.
- Marginal ROAS: how to scale ads with diminishing returns: A practical guide to marginal ROAS: why average ROAS misleads at scale, how diminishing returns work, and how to pick a profit-maximizing spend level.
- Target CPA: how to set acquisition targets from LTV and margin: A practical guide to target CPA: connect acquisition cost to LTV, contribution margin, and payback constraints (and avoid common mismatches).
- MER (blended ROAS): how to use it without fooling yourself: A practical guide to MER: what it is, how it differs from ROAS, how to compute break-even/target MER, and common pitfalls.