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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.

Updated 2026-01-23

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Incrementality Lift Calculator
Example: 100k exposed users (1,200 conv) vs 100k holdout users (900 conv), $50k spend

What lift means

Lift is the incremental outcome caused by ads compared to a no-ads baseline. A holdout test estimates that baseline by withholding ads from a comparable control group.

Core calculation (holdout scaled)

  • Holdout CVR = holdout conversions / holdout users.
  • Expected conversions without ads = exposed users * holdout CVR.
  • Incremental conversions = exposed conversions - expected without ads.
  • Incremental ROAS = incremental revenue / ad spend.

Decision rules (practical)

  • Use incremental profit, not reported ROAS, to decide what to scale.
  • If lift is near zero, treat the campaign as demand capture (not demand creation).
  • Prefer larger and longer tests to reduce noise; avoid changing many variables mid-test.

Common pitfalls

  • Holdout users still seeing ads (leakage).
  • Selection bias: exposed users differ from holdout users.
  • Ignoring variable costs (use contribution margin, not revenue).

FAQ

Should I use revenue, gross profit, or contribution margin-
Use contribution margin when possible because it reflects variable costs (fees, shipping, returns). Revenue-only lift can be misleading for low-margin products.
Can lift be negative-
Yes. It can occur due to noise, bad targeting/creative, or true cannibalization. Double-check randomization and that the holdout truly had no exposure.

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