Cannibalization: Is Paid Stealing Your Organic?

In one line

Sometimes a paid ad simply takes traffic that would have arrived organically for free. That is cannibalization, and it shows up most on ads aimed at people who already know you — brand search, retargeting.

Why it's risky

Performance reports credit every conversion to the ad that touched it last. If some of those users would have converted organically regardless, not subtracting that share makes ad efficiency look better than it really is.

How to confirm it

Observation alone can't prove cannibalization exists. A holdout test — randomly turning the ad off for part of your audience and comparing total conversions — is the real way to confirm it.

Cannibalization rate = organic conversions gained after pausing ÷ paid conversions lost

If paid conversions fall by 100 while organic rises by 70, the observed cannibalization rate is 70% and the remaining net increment is 30 conversions. Without random assignment or a comparable control, treat that rate as a diagnostic signal rather than a causal estimate.

Observation	What it may mean	Decision use
Paid falls while total stays flat	Organic substitution is plausible	Pause scaling and design a holdout
Total conversions also fall	Some net increment may exist	Recalculate incremental CPA or ROAS
Interval crosses zero	Current data cannot distinguish the effect	Do not translate it as no effect

Go deeper

Signals that suggest cannibalization, and how to confirm it, are covered in Diagnosing Cannibalization.

Frequently asked questions

How do you check for cannibalization?

The clearest test is turning ads off and watching how much organic rises. Pausing brand search campaigns for a set period or in selected regions surfaces the share that was being taken rather than created.

Is brand keyword advertising cannibalization?

Not entirely, but a large share of it is. Many people searching your brand name would have arrived anyway. Keeping brand terms in the same campaign as generic ones creates the illusion of strong overall efficiency.

If paid and organic both rise, is that not proof there is no cannibalization?

Moving together proves nothing on its own. Advertising may have created new demand, or the period may simply have been a seasonal peak. Separating them requires a counterfactual — a control group or a before-and-after design.

How do you calculate the cannibalization rate?

Compare the paid conversions lost when a brand campaign is paused against the organic conversions gained. Losing 100 paid while organic rises by 70 is a 70% cannibalization rate and 30 net incremental conversions — meaning that campaign's real CPA is roughly 3.3 times what the dashboard reports.