Publisher Monetization

Lazy Loading — Definition & Explanation

A technique that defers the rendering of ad units until they are about to enter the user's viewport. Lazy loading dramatically improves viewability scores (20-30 percentage point increase for below-fold units) and reduces wasted impressions.

How Lazy Loading Works

Intersection Observer APIs detect when ad containers approach the viewport and trigger ad calls at that point. This prevents below-fold ads from making bid requests before users can see them, improving viewability metrics and reducing latency.

Why Lazy Loading Matters for Publishers

Higher viewability scores directly increase CPMs. Most vCPM-buying advertisers pay 50-150% more for inventory that consistently achieves 70%+ viewability. Stellor Media's implementation guides include lazy loading best practices.

Frequently Asked Questions

How much does lazy loading improve viewability?

For below-fold placements, lazy loading typically improves viewability by 20-30 percentage points — from 30-40% to 60-70% viewable.

Does lazy loading affect fill rate?

Initially, lazy loading may reduce impression count (fewer below-fold impressions fire) but increases revenue per impression through higher viewability and CPMs.

Should I lazy load all ad units?

Yes for below-fold units. Above-fold placements can load eagerly to minimize latency for the most visible impressions.

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