Incremental Conversion Rate

Measured as

Incremental conversion rate = incremental conversions / total conversions

Misused when

• Assuming last-click conversions are all incremental.
• Ignoring conversion lag when measuring incremental impact.
• Using short windows that miss delayed conversions.
• Comparing incremental rate across channels with different test designs.
• Treating small lift tests as definitive for large budget shifts.
• Ignoring differences in average order value across test groups.

Operator takeaway

• Estimate with holdout or lift tests instead of attribution alone.
• Use the rate to adjust reported ROAS to true incremental ROAS.
• Track it by channel; incrementality varies by intent and audience.
• Use Incremental Conversion Rate only inside a stable attribution rule, conversion definition, and time window so campaign comparisons stay honest.
• If performance changes, check whether the metric moved for a real business reason or because the measurement setup changed underneath you.

Next decision

• Quantify the impact with Incrementality Lift Calculator if you need to turn the definition into an operating assumption.
• Read Attribution vs incrementality: what to trust, when, and how to test if the decision depends on interpretation, policy, or trade-offs beyond the raw formula.