Anchor Ads

What anchor ads are

Anchor ads (also called sticky ads or adhesion ads) are display ad units that stay fixed to the top or bottom edge of the browser viewport while the user scrolls through page content. Unlike standard banner ads that scroll out of view after the user passes them, anchor ads remain visible throughout the session.

The defining technical characteristic is CSS position: fixed with a top or bottom constraint — the ad container stays at its viewport position regardless of document scroll position. On mobile, bottom anchors are most common. On desktop, both top and bottom positions are used, though bottom anchors tend to perform better because they don't compete with navigation.

Google AdSense offers anchor ads natively as an auto ad format — when Auto Ads is enabled, Google's ad serving system decides whether to show an anchor unit based on user experience scoring. Independent publishers using header bidding stacks can implement anchor units manually through their ad server configuration.

Why anchor ads produce higher viewability

Viewability — the percentage of impressions where the ad was in view for at least 1 second (2 seconds for video) — is a critical quality signal in programmatic advertising. Viewability-sensitive buyers, including brand advertisers and many direct response buyers on open exchange, bid higher for inventory with strong viewability scores.

Standard in-content display ads achieve variable viewability depending on placement and page depth. Above-the-fold placements typically reach 60-80% viewability; below-the-fold placements can fall to 30-50% or lower. The drop-off depends on how many users scroll to the placement and whether the content there holds attention.

Anchor ads are continuously visible from the moment the page loads until the user closes the tab or navigates away. This means every impression served on an anchor unit that is in the viewport is viewable by definition — viewability scores regularly exceed 85-95%. This is among the highest achievable for any ad format outside video.

The consequence is meaningful for RPM: advertisers who set viewability thresholds in their bidding rules are more likely to bid on anchor inventory, and the higher viewability score increases bid density and average eCPM compared to equivalent standard placements.

Revenue contribution across site types

Anchor ads perform differently depending on content type and user behavior:

Long-form content sites (blog posts, guides, tutorials). Best fit for anchor ads. Users scroll through thousands of words; the anchor unit stays visible for the entire reading session. A 5-minute read generates a single anchor ad impression that is in view for the full 5 minutes. High session duration × high viewability = strong revenue contribution.

Short-form or paginated content. Less effective. If users typically spend 30 seconds on a page with minimal scrolling, the anchor ad provides limited session duration advantage over a standard banner, with added layout footprint.

Mobile-first audiences. Anchor ads on mobile devices need careful implementation. Bottom anchors compete with browser navigation (back button, address bar on scroll) on some devices. Publishers typically add a close button to reduce friction and avoid UX policy violations.

E-commerce and conversion-focused pages. Bottom anchor ads can conflict with cart buttons, checkout CTAs, and sticky add-to-cart elements. On transactional pages, the revenue from the anchor unit may be less than the conversion rate loss from adding another bottom-viewport element.

Implementation approaches

Google AdSense Auto Ads. The simplest path for AdSense publishers: enable Auto Ads in your AdSense account. Google's system decides when to show anchor ads based on its own user experience scoring, ad demand, and page context. Publishers have limited control but no implementation complexity.

AdSense anchor ad unit. Publishers can also create an explicit anchor ad unit in AdSense and implement it directly, without using Auto Ads for the rest of the page. This provides more control over when the unit shows and on which pages.

Programmatic through ad server. Publishers using a full header bidding stack (Google Ad Manager with Prebid.js or an equivalent) can create anchor placements and send them into the auction like any other unit. This gives the most control — custom sizing, custom bidding parameters, floor prices — but requires development work to implement correctly.

Managed networks (Ezoic, Mediavine). Publishers on managed ad networks typically have anchor ads available as a toggle in the network dashboard. These networks handle the technical implementation and split revenue according to their standard terms.

Ad quality and user experience policies

Anchor ads are subject to ad quality policies that limit how intrusive they can be:

Close button. Google's own policies and industry best practices require that anchor ads have a clearly visible close button so users can dismiss them. Anchor ads without a close button violate AdSense policy and are typically flagged for review.

Core Web Vitals. Anchor ads that appear after page load and shift existing content can cause Cumulative Layout Shift (CLS). Implementations that load the anchor unit within a pre-reserved space (the page layout includes a placeholder of the correct height from the first paint) avoid CLS impact. Poorly implemented anchors that push content up or down after load will cause CLS penalties that affect search ranking signals.

Coalition for Better Ads standards. The Better Ads Standards prohibit ads that cover more than 30% of the mobile screen. An anchor ad that takes up more than 30% of the vertical viewport on mobile fails this standard. Most anchor implementations use units of 50px or 90px height on mobile — well below the threshold.

Google Publisher Policies. Publishers using Google monetization cannot show more than one anchor ad at a time, cannot force users to interact with an anchor to continue using the site, and must ensure the close button is functional.

Core Web Vitals checklist

Before deploying anchor ads at scale:

1. Test for CLS. Use PageSpeed Insights or Chrome DevTools to measure Core Web Vitals including CLS with and without the anchor ad. The unit should appear within a pre-reserved space or load before any user-visible paint.
2. Check LCP impact. If the anchor ad script blocks page rendering, it may delay the Largest Contentful Paint. Load the ad script asynchronously.
3. Test mobile viewport. On devices with bottom navigation bars (iPhone with home indicator, Android with gesture navigation), a fixed bottom element can overlap with system UI or browser chrome. Test on real devices or accurate emulators.
4. Verify close button. Confirm the close button is visible, functional, and doesn't conflict with page elements.

Common mistakes

• Enabling anchor ads on checkout or high-conversion pages. Bottom sticky elements on transactional pages create friction that measurably reduces conversions. Exclude product detail pages, cart, and checkout from anchor ad serving rules.
• Implementing without Core Web Vitals testing. Anchor ads that cause CLS or loading delay affect both search performance and user experience. Measure before rolling out.
• Using anchor ads without a close button. Violates ad quality standards and generates user complaints, which feed back into ad network quality scoring.
• Assuming anchor ads will perform the same on desktop and mobile. Session duration, scroll depth, and viewport dynamics differ significantly by device. Analyze performance by device type and consider serving different units.

FAQ

How much RPM uplift should I expect from adding anchor ads? Varies substantially by site. Publishers with long-form content and high session duration typically see 10-30% RPM increases from adding anchor ads. Use the Ad Revenue Calculator to estimate the revenue impact before and after. Sites with short page sessions or high mobile bounce rates see smaller gains. Run a 7-day test comparing RPM with and without the anchor unit active.

Will anchor ads hurt my user experience or increase bounce rate? Well-implemented anchor ads with close buttons typically do not increase bounce rate significantly for content sites. The close button gives users control, which reduces the frustration effect. Poorly implemented anchors that are difficult to close or that overlap with navigation do increase bounce rates. Test UX metrics (scroll depth, session duration, bounce rate) alongside revenue metrics.

Can I run anchor ads alongside other sticky elements on my page? Be cautious with multiple sticky elements. A sticky header navigation, an anchor ad at the bottom, and a cookie consent banner that appears at load can collectively compress the visible content area significantly on mobile. Prioritize and test; not all sticky elements need to be active simultaneously.

Do anchor ads work with all ad networks? Standard display networks (Google AdSense, Ezoic, Mediavine) support anchor formats. Custom programmatic implementations through Google Ad Manager and Prebid.js can support anchor placements. Confirm with your specific ad network's documentation.

Is the RPM contribution from anchor ads additional to in-content ad revenue, or does it cannibalize existing impressions? Properly configured anchor ads are additive — they serve impressions during the scroll session that would not otherwise have an ad visible. They do not replace in-content units. However, if a user dismisses the anchor ad early, the remaining session has one fewer active impression. Net revenue impact is almost always positive for content sites with meaningful session duration.