Starting February 17, 2027, Google is changing how it measures display ad impressions in AdSense and Ad Manager. Affected inventory will move from Count-on-Download (COD) to Begin-to-Render (BTR), bringing Google's measurement closer to industry standard and more consistent across its platforms.
What's Actually Changing
Under the current Count-on-Download system, an impression is counted as soon as an ad starts downloading to a user's device, even if the visitor leaves the page before it ever renders.Under Begin-to-Render, Google will only count the impression once the ad creative has successfully loaded and started rendering on the screen. If a visitor navigates away before that point, the impression won't count. If the ad begins rendering while they're still on the page, it will.
In short, Google is shifting the question from "Did the ad start downloading?" to "Did it actually reach the screen?"
Which Inventory Is Affected
The change applies specifically to display banner inventory on desktop web, mobile web, and connected TV (CTV), the formats currently measured with Count-on-Download.Other formats are already BTR-compliant or use equivalent methodologies: native and interstitial display ads, app inventory (one-pixel measurement), and video (first-frame measurement). So this transition is really about bringing the one remaining format in line with everything else.
Why Google Is Making the Change
Google says Begin-to-Render is the industry-preferred approach and better reflects whether a user actually had a chance to see an ad, an ad that only started downloading isn't necessarily one a visitor ever saw. It also aligns Google's counting more closely with demand-side platforms and unifies methodology across inventory types, continuing a broader industry shift from counting at ad-serve, to download-start, to render-start.Impact on Impressions and Revenue
Google says publishers may see a decrease in reported display impressions after the transition, since impressions that used to count under COD, ads abandoned mid-load when a visitor clicked away, won't count under BTR. A site with 100,000 impressions today could report fewer after the switch, without any actual drop in traffic.Importantly, a drop in impressions doesn't automatically mean a proportional drop in revenue. This is purely a measurement change, not a statement about the value of an impression. The real financial effect depends on traffic, advertiser demand, visitor location, ad formats, and other factors, so it's worth watching revenue and RPM alongside impressions, rather than judging impact from impression counts alone.
Technical Factors That Affect Rendering
Because BTR only counts an impression once a creative renders, how efficiently your site and ads load starts to matter more.- Site performance: Heavy pages, oversized resources, and slow mobile loading give ads less time to render before a visitor leaves, worth cleaning up regardless, but more consequential now.
- Lazy loading/rendering settings: These control when ad assets fetch and render, affecting both COD and BTR counts. Widening rendering/fetching margins can make ads render earlier, but at the cost of more network and device resource use, Google recommends weighing that trade-off rather than changing settings reflexively.
- Creative complexity: More assets generally means longer download times. Synchronous scripts process assets sequentially (slower); asynchronous scripts can load them in parallel, improving the odds of reaching the render stage.
- Supply chain length: More "hops" through ad partners before reaching a creative can add delay, which is largely outside a publisher's control but explains why performance can vary across ad opportunities on the same site.
For Google Ad Manager Publishers: Estimating the Impact
Ad Manager publishers can compare their existing COD impressions against BTR impressions directly in reporting, using historical data starting after August 12, 2026. Relevant dimensions include demand channel, inventory format, inventory type, and device category, alongside ad server impression and ad server BTR impression metrics. This reporting option isn't available in the standard AdSense dashboard.What Publishers Should Do
No action is required, the transition happens automatically on February 17, 2027, with no code changes needed. It's a good moment to review site performance generally, but not a reason for major changes.If you do notice a sharp drop in impressions after comparing COD and BTR figures, Google recommends checking whether it's concentrated around a specific creative ID or buyer, and confirming those ads are actually rendering visibly on your pages. If an ad seems to be rendering correctly but isn't counting, contact your account manager or Google Support. Google also notes its measurement heuristics will keep evolving with further fixes for miscounting, so it's worth waiting on early data before overhauling anything.
Bottom Line
After February 17, 2027, judge performance by tracking traffic, impressions, revenue, and RPM together, not impressions in isolation. Some publishers may see impressions fall with little effect on revenue; others may see a bigger shift. The only reliable read will come from watching your own site's numbers once the new methodology is live.
Source: Google AdSense Help
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