What is real-time bidding (RTB)?
Real-time bidding (RTB) is a method of buying and selling digital ad impressions one at a time through automated auctions. When someone loads a web page, app or stream with an ad slot, the impression is offered to buyers, who bid based on its value to them. The winning ad is served, all within a fraction of a second.
RTB is the auction engine behind much of programmatic advertising, including the open auction and private marketplaces.
How real-time bidding works
Ad request: a user opens a page or app, and the ad slot calls the publisher's ad server or SSP.
Bid request: the SSP or exchange sends a bid request to connected DSPs. It describes the impression: site or app, ad size, device, approximate location and any available user identifiers, subject to consent.
Evaluation: each DSP checks the impression against its campaigns' targeting, budgets and frequency caps, then calculates a bid.
Bid response: DSPs return bids with the ad markup.
Auction: the exchange picks the highest valid bid above the floor price. Today this is almost always a first-price auction.
Ad delivery: the winning creative loads and the impression is recorded.
The whole process usually has to finish in roughly 100 to 200 milliseconds, depending on the exchange's timeout settings. Bids that arrive late are simply ignored.
Most RTB traffic uses OpenRTB, a protocol published by IAB Tech Lab that standardizes how bid requests and responses are structured, so DSPs and SSPs can connect consistently.
Why real-time bidding matters
Impression-level decisions: buyers pay only for impressions that match their targeting, rather than buying fixed packages.
Scale: RTB connects buyers to a very large pool of sites, apps and streaming inventory.
Price discovery: auctions set prices by demand, so buyers can control costs with bid strategy.
Optimization: bids can adjust automatically based on conversion likelihood, viewability or other goals.
Watch for the trade-offs: open RTB supply varies in quality, so brand safety controls, fraud filtering and supply path choices are part of any serious RTB setup.
RTB vs programmatic direct
RTB is auction-based: prices and wins vary impression by impression. Programmatic direct covers deals agreed in advance between buyer and seller, such as preferred deals and programmatic guaranteed, where the price is fixed and, for guaranteed deals, volume is reserved. RTB offers flexibility and scale; direct deals offer predictability and access to specific premium inventory. The open auction and private marketplaces both run on RTB; the difference is who is allowed to bid.
Real-time bidding with AdGeeks
AdGeeks traders buy RTB inventory on DV360, Amazon DSP and Adform, combining open auction reach with private deals where they fit the plan. We manage bids, floors, supply sources and brand safety settings, and optimize throughout the flight. To get started, request access.
