Real-Time Bidding (RTB)
Programmatic & DisplayDefinition
Real-time bidding (RTB) is an automated auction that decides which ad gets shown to a user, in the milliseconds while a page or app loads. Each impression is sold individually: advertisers submit bids through a demand-side platform, the highest relevant bid wins, and the winning creative renders before the user even notices a delay.
RTB is the engine underneath most programmatic display and video buying. When a user opens a page, the publisher sends a bid request through a supply-side platform (SSP) and ad exchange. That request carries signals such as the URL, device type, rough location, time of day and, where consent allows, audience data. On the buy side, demand-side platforms (DSPs) evaluate the request against each advertiser's targeting and budget, then respond with a bid. The exchange runs the auction, picks the winner and returns the creative, all inside roughly 100 milliseconds.
What makes RTB different from older media buying is that you no longer buy placements in bulk; you buy individual impressions based on who is about to see them. That shifts the question from 'which site do I want to appear on' to 'is this specific person, in this specific context, worth this specific price right now'. Most exchanges have moved from second-price to first-price auctions, which means you generally pay close to what you actually bid, so bid strategy and value rules matter more than they did a few years ago.
A bid request travels from the publisher's SSP to the ad exchange, which broadcasts it to connected DSPs. Each DSP scores the impression using your targeting, audience segments, frequency caps and bidding strategy, then returns a price. The exchange compares bids, the highest eligible bid wins, and the creative is served. Brand safety filters, viewability prediction and fraud detection all run within that same window, which is why DSP quality and inventory curation have a direct effect on results.
RTB matters because it puts granular control and measurement in your hands at the impression level. You can suppress users who already converted, raise bids for high-value audiences and cap frequency across the whole web instead of per site. The flip side is that performance depends heavily on transparency: opaque supply paths, made-for-advertising sites and hidden fees can quietly eat budget. Treating RTB as something you actively curate, not just switch on, is what separates profitable programmatic from wasted spend.
Example
A user opens a news article. The publisher's SSP sends a bid request to the exchange. Advertiser A bids 3 EUR CPM, advertiser B bids 4.20 EUR and advertiser C bids 4.50 EUR. In a first-price auction, advertiser C wins and pays roughly 4.50 EUR per thousand impressions; its banner renders before the page finishes loading.
On display inventory, RTB CPMs commonly sit between 1 and 6 EUR depending on format, audience and quality, while premium video and connected TV can run far higher. Knowing your CPM band per channel keeps bids realistic and stops you overpaying for low-value supply.
Related Terms
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Frequently Asked Questions
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The whole process, from bid request to winning creative being served, typically runs in under 100 milliseconds. It happens while the page or app is still loading, so the user does not perceive any delay even though a full auction took place behind the scenes.
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Programmatic is the broad term for automated ad buying. RTB is one method within it: an open auction where each impression is bid on individually. Programmatic also includes non-auction deals such as programmatic guaranteed and private marketplaces, where price and inventory are agreed in advance.
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It can be, but only with active curation. On open exchanges you can end up on low-quality or made-for-advertising sites if you do not apply inclusion lists, brand safety filters and fraud detection. Working with vetted inventory and a transparent DSP is what keeps RTB safe and efficient.
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