Published November 1, 2026 · By Ailumic # How do real-time ad auctions work? Every time someone opens an app or a web page that has an ad slot, that one slot is sold in an auction that lasts a fraction of a second: software bidding for advertisers names a price, the best bid wins, and the winner’s ad is shown before the page finishes loading. The advertiser pays only when its ad is actually shown. ## What is being sold Not a page, and not a week of space on it: **one viewing of one slot, by one person, right now**. When you open an app or a web page, each ad slot on it is offered for sale at that moment, and the auction is over before the page has finished drawing. The next person who opens the same page starts a new auction for the same slot, so a busy app sells each of its slots again and again all day, one viewing at a time. ## Who takes part - **The app or website** offers the slot, together with what it is allowed to say about the viewing: the kind of app or page, the size and position of the slot, the device, roughly where it is, and whether the person has opted out of interest-based ads. The offer carries no name and no email address. - **An ad exchange** runs the auction. It sends the offer to the buyers connected to it, collects their bids, picks the winner and tells the app or page which ad to show. - **Buyers** are software that bids on advertisers’ behalf. Each buyer holds many advertisers’ campaigns, and for each offer it decides, in a fraction of a second, whether any of them fits and what the viewing is worth to that advertiser. Software like this is called a demand-side platform. Ailumic is one. ## What decides the winner The best bid wins, and the winner’s ad is sent back to be shown. What the winner pays depends on the exchange’s rules: on some, the winner pays what it bid; on others, a price just above the next-best bid. Either way the advertiser is charged for that viewing only if the ad is actually shown. A bid that loses costs nothing, and so does a slot the buyer decides not to bid for. ## What a bid is based on A buyer does not know who is looking. It knows the slot and its context, and from those it estimates two things: how likely this viewing is to do what the advertiser wants — a click, a visit, a sign-up — and what the auction is likely to clear at. Then it bids what the viewing is worth to that advertiser, and no more. The estimate comes from what similar viewings did before: the placement, the time of day, the kind of app or page, the area. Ailumic’s models are built to update that estimate as results arrive rather than once a week, so a slot that brought clicks this morning is bid for differently this afternoon. Every run teaches the next. ## What it means for a small budget The slot does not know how big the advertiser is. The same auction sells the same viewing to a one-person shop and to the largest brand in the country; a smaller budget simply wins fewer viewings. That is why no minimum is needed. Start with what you have — there is no minimum. You pay only for ads that are actually shown. ## Where Ailumic fits Ailumic is the buyer in this story, for you. You set a budget, an area, how many days the ad should run and the placements you want; Ailumic bids for your ad whenever a slot fits, pays only when it wins, and shows you afterwards where the ad ran and what it did. The price is in front of you before you confirm, and nothing runs until you do. Ailumic is opening to its first advertisers in the United States and is not buying ads yet; the home page says where we are. The technical account — the protocol, the deadline, the checks made before a price is computed — is under [the hood on the How it works page](https://www.ailumic.com/platform/#under-the-hood). Read next - [What is a CPM in advertising?](https://www.ailumic.com/guides/what-is-a-cpm/) - [Banner, native or full-screen: which ad format should a small business choose?](https://www.ailumic.com/guides/banner-native-or-full-screen/) - [How Ailumic works](https://www.ailumic.com/platform/) Ready to try it? Ailumic is opening to its first advertisers in the United States. [Get early access](https://www.ailumic.com/start/) Guides ## More questions, answered first. - ### [What is a CPM in advertising?](https://www.ailumic.com/guides/what-is-a-cpm/) CPM is the price of showing an ad one thousand times. Why ad space is priced per viewing, what moves the price, and why Ailumic publishes no price list. Updated November 1, 2026 - ### [Banner, native or full-screen: which ad format should a small business choose?](https://www.ailumic.com/guides/banner-native-or-full-screen/) A banner runs beside the content, a native ad sits in the feed, a full-screen ad fills an app between pages. How to pick one for the ad you have. Updated November 1, 2026 - ### [How much should a small business spend on ads to start?](https://www.ailumic.com/guides/how-much-to-spend-on-ads/) Size a first ad budget by what you can afford to learn from, not by a rule of thumb: enough to run a full week, small enough that a lesson with no sale is fine. Updated November 1, 2026 - ### [How do I read an ad report?](https://www.ailumic.com/guides/how-to-read-an-ad-report/) Read an ad report in order: times shown, clicks, cost, then where and when it ran. What the click-through rate tells you, and what to change next. Updated November 4, 2026 - ### [How long should an ad campaign run?](https://www.ailumic.com/guides/how-long-should-an-ad-run/) Run a first ad for a full week and no longer than it takes to learn one thing. Why a week, why not months, when to stop early and when to add budget. Updated November 1, 2026 - ### [What is programmatic advertising?](https://www.ailumic.com/guides/what-is-programmatic-advertising/) Programmatic advertising is ad space bought by software, one viewing at a time, in an auction. What it replaced and what it means for a small business. Updated November 7, 2026 - ### [What is a DSP, or demand-side platform?](https://www.ailumic.com/guides/what-is-a-dsp/) A DSP is software that bids for ad space on an advertiser’s behalf. How it differs from an ad exchange and a supply-side platform, and where Ailumic fits. Updated November 7, 2026 - ### [How do ads in mobile apps work?](https://www.ailumic.com/guides/how-mobile-app-ads-work/) An app sets aside ad slots, sells each one in an auction as it is about to appear, and draws the winning ad. What an advertiser chooses and sees afterwards. Updated November 7, 2026 - ### [How do I write an ad for my small business?](https://www.ailumic.com/guides/how-to-write-an-ad/) Write one message for one kind of person, say what to do next, and cut the rest. How to fit it to a banner, native or full-screen ad, and when to rewrite. Updated November 7, 2026