RTB
Real-time bidding. The auction process by which individual impressions are bought and sold as a page or app loads.
What is RTB?
RTB, or real-time bidding, is the auction mechanism behind much of programmatic advertising. Each time a page, app or stream has an ad opportunity, a supply-side platform or exchange sends a bid request to multiple buyers, who decide in a fraction of a second whether to bid and how much, based on the impression’s context and their campaign goals. The highest eligible bid wins and its ad is served. RTB is used in the open auction and in private marketplaces, and its messages are usually formatted according to the OpenRTB specification. Header bidding adds another layer by running several such auctions in parallel.
How RTB works
A bid request describing the impression is sent to buyers, who respond with bids within milliseconds; the winning ad is served.
- An ad opportunity occurs and the publisher’s SSP or exchange builds a bid request.
- The request is sent to connected DSPs, which compare it against their campaigns’ targeting and budget.
- DSPs return bids within a strict time limit, often a few hundred milliseconds or less.
- The auction picks the winning bid above the floor, the ad is served and the winner is charged.
Why it matters
It allows each impression to be valued individually instead of buying placements in bulk.
For advertisers
RTB lets buyers value and bid on each impression individually, focusing spend where data suggests it will perform.
For publishers
Competition among many buyers for each impression helps publishers find the market price of their inventory.
Practical example
While an article loads, an auction decides which advertiser’s banner appears.
Key considerations
- The speed of RTB depends on fast, reliable infrastructure; slow responses mean missed auctions.
- Bid requests can carry user data, so consent and privacy rules shape what may be shared.
- Most RTB auctions now use first-price rules, which changes how buyers set bids.
More Programmatic Advertising terms
Frequently asked questions
Is RTB the same as programmatic advertising?
No. RTB is one auction-based method within programmatic, which also includes guaranteed and fixed-price deals.
How fast does RTB happen?
The whole auction typically completes within the time it takes a page or app screen to load, with buyers given a fraction of a second to respond.
Does RTB use first-price or second-price auctions?
Most of the industry has moved to first-price auctions, where the winner pays its bid rather than just above the next highest.