Programmatic Advertising 101: How Media Buying Actually Works
An ad impression is bought and sold in roughly the time it takes to blink, by five intermediaries you never signed a contract with. Here is the chain, in order, with the fee at each link.
Programmatic advertising is usually explained with a diagram nobody reads. The simpler version: when a page loads, an auction runs for the space beside the article, and by the time the pixels appear a buyer, a seller and three intermediaries have each taken a position and a fee. Understanding the order of that chain is the difference between buying media and being sold it.
The chain, link by link
- The advertiser sets a budget, an audience and a maximum price.
- The DSP (demand-side platform) is the buying interface. It receives bid requests, decides what each impression is worth and submits a bid. It charges a percentage of media spend.
- The exchange runs the auction and matches buyers to sellers. It takes a cut of the winning bid.
- The SSP (supply-side platform) represents the publisher, connects its inventory to exchanges and manages floor prices. It also takes a cut.
- The publisher receives what remains and serves the ad.
Alongside these sit verification vendors, data providers and identity resolution services, each with a fee of their own. None of them is illegitimate. The problem is cumulative: a chain of reasonable percentages produces an unreasonable total.
Header bidding and why it changed everything
Publishers used to run a waterfall: offer inventory to the highest-paying network first, then the next, and so on until something filled. It was slow and it systematically underpriced inventory, because the first network in the queue never had to compete.
Header bidding replaced the queue with a simultaneous auction. Multiple demand sources bid at the same time before the ad server makes its decision, and publisher yield rose materially as a result. The cost was complexity: an impression can now reach a buyer through several different paths at once, at different prices, with different fees deducted along the way. Almost every transparency problem in modern programmatic traces back to that duplication.
First-price auctions
The industry moved from second-price auctions, where the winner paid one cent above the second-highest bid, to first-price, where the winner pays exactly what it bid. The shift was necessary — header bidding made second-price mechanics unworkable across parallel auctions — but it changed buying strategy fundamentally.
Under first-price, overbidding costs money directly. That is why bid shading, the practice of estimating the minimum bid needed to win and submitting that instead of your true valuation, moved from an optimisation nicety to a core DSP function. If your DSP cannot explain its shading logic, you are systematically overpaying.
Private deals and where they help
| Deal type | How it works | Best for |
|---|---|---|
| Open auction | Anyone can bid on available inventory | Reach and efficiency at scale |
| Private marketplace (PMP) | Invitation-only auction via a deal ID | Quality control and brand safety |
| Preferred deal | Fixed price, non-guaranteed volume, first look | Priority access to specific inventory |
| Programmatic guaranteed | Fixed price and fixed volume, automated | Replacing insertion orders with pipes |
The practical rule: use the open auction for scale, private marketplaces where inventory quality genuinely varies, and programmatic guaranteed where you would previously have signed a direct insertion order. Advertisers who moved everything into PMPs to feel safer usually paid a premium for inventory they could have bought openly.
Where the money leaks
Four leaks account for most of the loss between budget and attention.
Intermediary stacking. Each additional hop takes a percentage. Reselling — where one intermediary buys inventory and offers it again through another — multiplies this invisibly.
Made-for-advertising inventory. Sites built to arbitrage cheap traffic against ad revenue. They are technically viewable, technically brand-safe by most definitions, and worth almost nothing in attention terms.
Duplicate paths. The same impression offered through several SSPs at once. You may bid against yourself, and you certainly pay different fees depending on which path wins.
Unverified sellers. This is what ads.txt and sellers.json exist to solve: publicly declaring who is authorised to sell a publisher's inventory and who sits in the chain. Buying from paths that fail this check is avoidable and still common.
Supply path optimisation
The highest-return project available to most advertisers is not a new targeting strategy; it is deliberately reducing the number of ways an impression can reach you. Pick a limited set of verified paths, block resold inventory, enforce ads.txt and sellers.json checks, and measure the fee taken at each remaining hop.
It is unglamorous, it produces no case study, and it routinely recovers more working media than a quarter of creative optimisation. Ask your agency for a supply path report by seller, and if that report cannot be produced, you have found the problem.
Note on data. Fee structures vary widely by platform, market and negotiated terms, and most intermediaries do not disclose their take rate publicly. Figures circulating in industry research are typically estimates derived from limited samples. Use log-level data from your own campaigns rather than published averages when assessing your own supply chain.
Sources
The claims in this article rest on the documents below. Each is linked to what it establishes, so you can check any statement against its origin rather than taking ours for it.
- IAB Tech Lab, ads.txt specification v1.1 (August 2022) — the authorised-seller file every publisher in the chain is expected to serve
- IAB Tech Lab, app-ads.txt v1.0 — the same mechanism for in-app inventory
- IAB Europe, adoption of supply chain transparency standards — how far ads.txt, sellers.json and the SupplyChain object are actually deployed in Europe
- ANA, Programmatic Media Supply Chain Transparency Study (December 2023) — what the chain costs in practice: 36 cents of the dollar reaching the consumer
Frequently asked questions
What is programmatic advertising in simple terms?
It is the automated buying and selling of advertising space through real-time auctions. When a page loads, an auction runs for the space in milliseconds: buying platforms bid on behalf of advertisers, selling platforms represent publishers, and an exchange matches them. The ad appears as the page finishes rendering.
What is the difference between a DSP and an SSP?
A DSP is the buy side — advertisers and agencies use it to bid on impressions across many publishers. An SSP is the sell side — publishers use it to expose their inventory to demand and manage floor prices. Both take a fee, and both sit between the advertiser's budget and the publisher's revenue.
What is header bidding?
A technique that lets publishers offer inventory to several demand sources simultaneously before the ad server decides, replacing the old sequential waterfall. It raised publisher revenue significantly but made the supply path far more complex, which is the root of most transparency problems in programmatic today.
What are ads.txt and sellers.json?
Public files that declare who is authorised to sell a publisher's inventory and identify the intermediaries in the chain. They exist to prevent domain spoofing and unauthorised reselling. Buying only from paths that pass these checks is basic hygiene and still not universal.
How much of a programmatic budget reaches the publisher?
Materially less than most advertisers assume, once DSP, exchange, SSP, data and verification fees are deducted, and before accounting for low-quality inventory. Industry studies place the share reaching the consumer well below half. The only reliable way to know your own number is log-level analysis of your own campaigns.