What is ad spend?

Gross and net

The word covers two different numbers, and contracts turn on which one is meant.

Gross spend is everything leaving the advertiser: media, platform fees, agency commission, data and verification costs.

Net spend, sometimes working media, is what actually reaches the inventory.

The gap can be substantial. Computing efficiency metrics on net while budgeting on gross makes a campaign look better than the business experienced, which is why any ratio — ROAS, CAC — should state which it used.

Why aggregating it is hard

• Currencies and timing. Platforms report in different currencies with different billing cycles.
• Definitional drift. One platform's spend includes fees, another's does not.
• Credits and rebates that land in a later period than the spend they relate to.
• Taxonomy mismatch. The same campaign named differently in five systems.
• Reconciliation lag, where reported spend is revised after the fact.

Cost aggregation

Cost aggregation is the discipline of resolving all of that into one comparable view. It sounds like plumbing and it determines whether any efficiency metric you compute is true, because every one of them has spend in the denominator.

The failure is usually silent: a platform's fees excluded here and included there, and a channel looks 20% more efficient than it is. Fixing it is unglamorous and pays for itself immediately.

Where AI spend sits today

For most advertisers AI media is a small line and a fast-growing one. Two habits are worth establishing while it is small.

Track it as its own channel rather than folding it into display or programmatic — blended it disappears, and the distinct behaviour that makes it worth buying is invisible. And budget for measurement alongside it: a holdout is a cost of the channel rather than an optional extra, because without one the reported numbers will understate what it is doing.