How software buys ad space in the time a page takes to load, where the money goes on the way, and the eight questions a brand should put to its agency before the next quarter's budget is signed off.
Programmatic advertising explained in one sentence: it is the buying and selling of ad space by software, in an auction that runs in the time it takes a web page to load. Instead of a media buyer phoning a publisher and agreeing a price for a slot, an advertiser’s bidding platform looks at each individual impression, decides what it is worth and bids for it, thousands of times a second.
That is the whole idea. Everything else, the acronyms, the intermediaries and the fees, is plumbing built around it. The plumbing is where the money goes missing, which is why this explainer spends as long on the supply chain and the questions a brand should ask as it does on the mechanics. Around 78 per cent of UK digital display is now traded this way, according to the IAB UK, so it is not a niche any marketer can leave to the agency.
Programmatic is a method of buying, not a type of ad. A banner on a news site, a pre-roll before a YouTube video, a 30-second spot on a streaming service and a sponsored product on a supermarket’s app can all be bought programmatically. What they share is that the transaction is automated and the decision to buy is made impression by impression, using data about the person, the page and the moment.
The contrast is with the direct buy, where a publisher sells a fixed number of impressions or a fixed period on a page at a negotiated price. Direct buying still exists and still makes sense for takeovers, sponsorships and anything where the context is the point. Programmatic replaced it for the bulk of display because it lets an advertiser buy the audience wherever it happens to be rather than guessing which sites it visits.
Four pieces of software do the work. The advertiser, or its agency, uses a demand-side platform (DSP) to set budgets, targeting and bids. The publisher uses a supply-side platform (SSP) to offer its ad slots for sale and to set the minimum it will accept.
An ad exchange sits between them and runs the auction. An ad server, on each side, delivers the actual creative and counts what happened.
The sequence for a single page view runs like this. You open a page and the publisher’s SSP announces that an ad slot is available, along with whatever it knows: the page, the device, the country, sometimes an identifier for you. That bid request goes to an exchange, which forwards it to dozens of DSPs. Each DSP checks whether you match any of its advertisers’ campaigns, decides a price, and bids.
The exchange picks a winner, the winning DSP’s ad server sends the creative, and the ad appears. The whole round trip is measured in milliseconds and is invisible to the reader. This is real-time bidding, usually shortened to RTB, and it is the part most people mean when they say programmatic.
People search for “programmatic vs display” as if they were rivals, but they are different axes. Display describes the format: a visual ad unit on a website or in an app, as opposed to search, audio or television. Programmatic describes how the space was bought. Most display is now programmatic, and a growing share of video, audio and outdoor is too, so the useful distinction is between programmatic and direct, not programmatic and display.
The other confusion is with paid social. Meta and TikTok run their own auctions inside their own walls, using their own data, and you buy through their own tools. That is automated and auction-based, but the industry usually reserves the word programmatic for the open web and for connected TV, where independent DSPs and SSPs are involved and the advertiser has a choice of technology.
Not all programmatic is an open auction. The trade splits deals into four types, and the further down the table you go the more the deal resembles an old-fashioned direct buy with the paperwork automated.
| Deal type | Who can bid | Price | Inventory | Best for |
|---|---|---|---|---|
| Open auction (RTB) | Anyone with a DSP | Set by auction | Not guaranteed | Scale and low cost, with the most risk |
| Private marketplace (PMP) | Invited buyers only | Auction above a floor | Not guaranteed | Named publishers at an agreed minimum |
| Preferred deal | One buyer, first look | Fixed | Not guaranteed | First refusal on premium slots |
| Programmatic guaranteed | One buyer | Fixed | Guaranteed volume | Sponsorships and must-have placements |
PMPs and programmatic guaranteed matter more than their share of spend suggests. When ISBA and PwC re-ran their supply chain study in 2022, PMP deals matched from buyer to seller at a rate above 70 per cent and the unexplained money in them was under 1 per cent, because a deal ID travels with every impression and both sides can see it. The open auction is cheaper per thousand and far harder to audit.
In May 2020 ISBA, the UK advertisers’ body, published a study by PwC that tracked £100 million of programmatic spend from 15 advertisers through 12 agencies, five DSPs and six SSPs to 12 premium publishers. It found that publishers received 51 per cent of what advertisers spent. Of the rest, about a third, or 15 per cent of the total, could not be attributed to anyone at all, a figure the report called the “unknown delta”.
The ISBA executive summary is worth reading for its second finding, which got less attention. Of 267 million impressions served from the study’s advertisers to its publishers, only 31 million, 12 per cent, could be matched end to end, because the data on each side was too inconsistent to line up. The supply chain was not just expensive. It was unauditable.
The follow-up, published in January 2023 with a standard audit permission letter and data field list in place, matched 58 per cent of impressions, cut the unknown delta to 3 per cent and lifted the publisher’s share to 65 per cent. That is genuine progress, and it was earned by advertisers demanding log-level data in their contracts rather than by the technology getting cheaper.
The American figures are worse. The ANA’s Programmatic Media Supply Chain Transparency Study, published in December 2023 from $123 million of spend across 21 advertisers, concluded that only 36 cents of every dollar entering a DSP reached a consumer in a viewable, measurable ad on a legitimate site. Its 2024 benchmark with TAG TrustNet, summarised by the WFA, moved that to 44 cents, with participating advertisers halving the number of domains they bought, from 44,000 to 22,634.
The cheapest impressions in an open auction are cheap for a reason. Some are outright fraud: bots loading pages, ads stacked invisibly on top of each other, apps spoofing the identity of premium publishers. The bigger and less obvious problem is the “made for advertising” site, a page built to be bought programmatically rather than to be read, stuffed with ad units and fed by paid traffic from social platforms.
The ANA’s 2023 study found MFA sites took 21 per cent of impressions and 15 per cent of spend, and that every one of the 21 advertisers had bought some. In September 2023 the ANA, the 4A’s, ISBA and the WFA published a joint definition, which starts with an ad-to-content ratio of 30 per cent or more on desktop and adds paid traffic sourcing, low-value templated content and aggressive refresh. A year later the ANA’s benchmark put average MFA spend at 6.2 per cent, and the median at 1.1 per cent, among the advertisers who had acted on it.
The lesson is not that programmatic is a scam. It is that a DSP set to find the cheapest available impressions will find them, and the cheapest impressions on the internet are the worst ones. Inclusion lists, a curated set of a few hundred sites the brand has actually looked at, cost more per thousand and deliver more per pound.
The third-party cookie is how most open-web targeting, retargeting and frequency capping has worked since the 1990s, and its death was announced by Google in January 2020 with a two-year deadline. The deadline slipped three times. On 22 April 2025 Google’s Anthony Chavez wrote that Chrome would keep its existing cookie controls and “will not be rolling out a new standalone prompt”, which ended the deprecation without quite saying so.
On 17 October 2025 the same author retired most of the Privacy Sandbox, including Topics, Protected Audience and the Attribution Reporting API, citing “low levels of adoption”. The same day the CMA released Google from the commitments it had accepted in 2022 and closed its four-year investigation, because there was no longer a cookie removal to police. Safari and Firefox have blocked third-party cookies for years, so a meaningful minority of UK browsing was already cookieless.
The practical position in September 2026 is therefore stable but split. Cookies work in Chrome, still the majority browser, and do not work elsewhere. Advertisers who built first-party data, contextual targeting and clean-room measurement during the false alarm are better placed than those who waited, and the same tools are what retail media and connected TV run on anyway.
Two channels are pulling programmatic away from the banner. The first is connected TV: ITVX, Channel 4, Sky, Netflix and Amazon all sell their ad breaks with programmatic pipes attached, and the IAB UK reported that what it calls TV+ made up more than a third of the £4.3 billion spent on video in the first half of 2025. The auction is usually private or guaranteed rather than open, the inventory is scarce, and the buyer is often the same TV planner who bought the linear spots.
The second is retail media, which the IAB UK put at £3.8 billion in 2025, up 18 per cent. Tesco, Boots, Sainsbury’s and above all Amazon sell ads targeted with what people actually buy, on their own sites and increasingly on other people’s. The FTC’s August 2026 case against Amazon is the first serious test of how those auctions are run: the complaint alleges that Amazon advertised a second-price auction while charging Sponsored Products advertisers their own winning bid around 80 per cent of the time by 2024, through a hidden “soft reserve price”. Amazon disputes it and says such reserves are standard practice.
The open-web exchange has had its own reckoning. In April 2025 a US federal court found Google had illegally monopolised the publisher ad server and ad exchange markets, and on 2 September 2026 Judge Leonie Brinkema declined to order the sale of AdX but imposed behavioural remedies, including sharing real-time bid data with rival ad servers and ending first-look and last-look privileges. Whether that changes the price of an impression in Britain is an open question.
None of the above requires a marketer to understand a bid request. It requires the right questions at the start of the contract, in writing, and the same ones again every quarter. These are the ones that separate an agency running a transparent programme from one selling a black box.
The measurement question is the one that matters most, and it belongs in the plan before a pound is spent, as we argued in our guide to approaching a campaign. Programmatic reports faster and in more detail than any medium in history, which makes it easy to optimise towards the wrong number with great precision. Only fewer than half of brands have a defined effectiveness function to notice.
Google Search ads are bought in an automated auction but are not usually called programmatic, because the trigger is a keyword rather than an audience and the inventory belongs to one company. Google’s Display & Video 360 is a DSP and its Display Network is programmatic in the ordinary sense.
Most DSPs charge a percentage of media spend, and the ANA’s studies put DSP and SSP fees together at roughly 29 cents of every dollar in 2023. Data, verification and agency fees come on top, which is why the working media figure and not the DSP fee is the number to ask for.
It can be, in the way any medium can be: when the creative is right, the audience is real and the measurement is honest. Its weakness is not the auction but the temptation to chase the cheapest impressions and the fastest-reporting metric, both of which reward the worst inventory.
Not in Chrome, as of September 2026. Google dropped its plan to remove them in April 2025 and retired most of the replacement technology in October 2025. Safari and Firefox already block them, so a meaningful share of browsing is cookieless regardless.
He plans, buys and reviews advertising for a living, and helps score campaigns on the site against the same five Crown Score criteria alongside other authors and contributors.
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