RTB (Real-Time Bidding)

Quick Definition: Automated auction system that buys and sells ad inventory per impression in ~100 milliseconds.

What is RTB

Real-time bidding is how most digital ads get bought today. Each time a user opens an app or webpage, an auction happens. Advertisers bid on that exact impression. Highest bidder wins. Ad serves instantly.

The entire process happens faster than a blink.

RTB replaced the old model where advertisers bought ad inventory in bulk upfront. Now you bid per impression, targeting specific users based on data signals like demographics, behavior, and context. The IAB Tech Lab’s OpenRTB protocol standardizes how these auctions work across the industry.

How It Works

The 100ms auction:

1. User opens app – Triggers ad request
2. Bid request sent – Goes to ad exchange with user data
3. DSPs evaluate – Demand-side platforms analyze user signals
4. Bids submitted – Each DSP submits max bid for that impression
5. Winner determined – Highest bid wins in milliseconds
6. Ad serves – Winning creative displays to user

All of this before the app even finishes loading.

DSPs use algorithms to decide bid amounts based on advertiser goals, user value, and campaign budgets. Better targeting data means smarter bids.

Mobile RTB (In-App Bidding)

Mobile gaming uses in-app bidding, which is RTB optimized for apps.

Desktop calls this “header bidding.” Mobile calls it “in-app bidding.” Same core concept.

In-app bidding lets multiple ad networks compete for your inventory simultaneously. Before in-app bidding, mobile used waterfalls. Sequential auction tiers where networks got first dibs based on fixed priority. Inefficient and left money on the table. AppLovin’s in-app bidding technology helped drive industry adoption of this unified auction model.

In-app bidding runs one unified auction. Every network bids at once. Highest CPM wins regardless of waterfall position.

Why mobile games care:

• Higher eCPMs (more revenue per impression)
• Better fill rates (fewer unfilled ad slots)
• Fairer competition (merit-based, not priority-based)
• Faster optimization (real-time price discovery)

RTB vs Programmatic

Programmatic = All automated ad buying (includes direct deals, private marketplaces, RTB)

RTB = One type of programmatic buying (open auction model)

Think of programmatic as the category. RTB is the specific auction method within it.

Other programmatic methods include programmatic direct (fixed price, automated) and private marketplaces (invitation-only auctions). RTB is the open market where anyone can bid. AdExchanger tracks how programmatic buying continues to evolve.

Market Size

RTB dominates digital advertising spend:

• $18.8B in 2024
• $92.6B projected by 2033
• 18.41% CAGR over next decade, per IMARC Group’s Real-Time Bidding Market report
• 91.3% of US digital display ad dollars went programmatic in 2024

Translation: If you’re buying digital ads, you’re probably using RTB whether you realize it or not.

Common Mistakes

Confusing RTB with programmatic RTB is a subset. Not all programmatic is RTB.

Assuming RTB means cheap inventory RTB is a buying method, not a quality indicator. Premium inventory gets sold via RTB too.

Ignoring bid strategy Your max bid matters. Bid too low, you lose impressions. Bid too high, you waste budget. Algorithms help but strategy matters more.

Not testing creative fast enough RTB gives you speed. Your creative production needs to match that speed or you’re bottlenecked.

Treating all impressions equally RTB’s power is precision. User at level 50 is worth more than user at level 2. Bid accordingly.

Related Terms

• DSP (Demand-Side Platform) – Platform advertisers use to bid on RTB inventory
• SSP (Supply-Side Platform) – Platform publishers use to sell inventory via RTB
• Programmatic Advertising – Automated ad buying (RTB is one type)
• In-App Bidding – Mobile-specific RTB implementation
• Waterfall – Old sequential auction model RTB replaced
• eCPM – Effective cost per thousand impressions

External Resources

• Adjust: Real-Time Bidding
• AppLovin: RTB Glossary
• Amazon Ads: Real-Time Bidding Guide

Frequently Asked Questions

What does RTB stand for?

RTB stands for Real-Time Bidding, the automated auction system that buys and sells ad inventory one impression at a time, in about 100 milliseconds per auction.

How fast is real-time in RTB?

Around 100 milliseconds. The whole auction, bid request, DSP evaluation, winning bid, and ad serving, completes before the app or page even finishes loading.

What’s the difference between RTB and programmatic advertising?

Programmatic is the umbrella term for all automated ad buying, including direct deals and private marketplaces. RTB is one type of programmatic buying specifically: the open auction model where impressions sell to the highest bidder in real time.

Does RTB work for mobile games?

Yes. Mobile gaming uses in-app bidding, which is RTB built for apps. It replaced the old waterfall model where networks got sequential priority, running one unified auction instead where the highest bid wins regardless of network position.