Real-Time Bidding (RTB) is an automated auction that decides which ad to show in the milliseconds before a slot loads. Every time an impression becomes available, advertisers bid for it, the highest bid wins, and the winning ad renders, all without a human touching the transaction. RTB is the engine underneath programmatic advertising.

How it works

When a user opens a screen with an ad slot, the publisher's supply-side platforms, or SSPs, send details about that impression to an Ad Exchange. The exchange passes the opportunity to advertisers, who bid through demand-side platforms, or DSPs, that evaluate the impression against their targeting and budgets and return a price. The exchange collects the bids, picks the winner, and the ad loads. This whole round trip finishes in well under a second, which is why the value of each impression can be priced individually rather than sold in bulk.

RTB vs. in-app bidding

RTB grew up on the web, where SSPs, exchanges, and DSPs trade impressions across the open market. In-App Bidding applies the same per-impression auction idea inside a mobile app's mediation stack, letting demand sources compete at once instead of queuing in a waterfall. The mechanics rhyme, since both price each impression live rather than in advance. The difference is the setting, with classic RTB running across the programmatic open market and in-app bidding running within an app's own set of connected sources.

Why RTB matters for publishers

RTB lets you sell each impression for close to what it is truly worth to the highest bidder, rather than accepting a flat rate negotiated in advance. It opens your inventory to a broad pool of programmatic demand, which lifts competition and prices, and it does so automatically once the plumbing is in place. For most apps, programmatic demand delivered through RTB is a core part of filling inventory and earning a fair price for it.

How an offerwall complements RTB

RTB prices passive impressions in an auction. An offerwall does something different, monetizing intent by paying users for completed offers rather than for views. Because the two earn in unrelated ways, an offerwall does not compete with your RTB demand, it complements it. Programmatic auctions capture value from ordinary impressions across your traffic, while the offerwall captures value from motivated users who choose to engage, and together they cover more of your audience than either could alone.

Common misconceptions

• RTB and programmatic are the same thing. RTB is one way to buy programmatically. Programmatic also includes direct and guaranteed deals that skip the open auction.

• The highest bid always wins outright. Floors, deal priorities, and brand-safety filters can all override raw price.

• More demand always means higher pay. Without sensible price floors, extra low-quality bidders can crowd inventory without lifting your yield.