What’s more important: conversions, or incremental conversions?

Your retargeting campaign just claimed 1,000 conversions. Congratulations—except 800 of those people were going to buy anyway. So did you actually generate 1,000 sales, or 200?

The credit-stealing problem

A "conversion" is any sale your marketing claims credit for. An "incremental conversion" is a sale that only happened because of your marketing—one that wouldn't have occurred otherwise.That distinction is everything.

Ad platforms are designed to claim credit, not prove causation. Someone sees your Meta ad, ignores it, Googles your brand name three days later, and buys. Meta takes credit. Google takes credit. But that customer already knew who you were—they were buying regardless. The conversion was real, but the incremental value of those ads? Possibly zero.

Incrementality asks the only question that matters: What would have happened if we hadn't run this campaign?

How you measure it

You measure incrementality with holdout tests —scientific experiments where you show ads to one group and withhold them from another, then compare conversion rates.

If the exposed group converts at 5% and the holdout converts at 4%, your ads generated a 1% incremental lift. That's your true contribution. Everything else is noise.

Here's the uncomfortable truth: studies show retargeting campaigns—the darlings of performance marketing—often have the lowest incrementality. You're paying to advertise to people already mid-purchase. Branded search? Same problem. You're bidding on your own name to capture customers who were already coming.

Example

A DTC brand runs Meta ads. Platform attribution says: 481 purchases. Incrementality analysis says: 171 were actually incremental. That's a 64% gap between what the platform claims and what marketing actually caused. Imagine reallocating budget based on the wrong number.

Takeaway

Conversions tell you what happened—incremental conversions tell you what your marketing actually caused.