In Google Ad Manager and AdSense, impression measurement for display inventory will switch from the count-on-download (COD) to begin-to-render (BTR) methodology beginning February 17, 2027.
In this article:
- Overview
- Benefits of begin-to-render for display ads
- Timeline for the change
- Preparing for the change
- Best practices
- About impression counting and MRC accreditation
- FAQ
Overview
Count-on-download involves counting an impression when an ad starts to download to a user’s device. Begin-to-render counts an impression when the ad creative has successfully loaded and has started to render on the user’s device. Begin-to-render presents a greater likelihood that the user can view the ad. To learn more about BTR, visit the IAB’s desktop display measurement guidelines.
Currently, Ad Manager and AdSense already use or are compliant with begin-to-render for native, app, and video inventory impression counting. The shift to count display ads via BTR unifies our impression counting methodologies.
Here’s a breakdown of the current and future methodology use:
| Inventory type | Current methodology | Future methodology |
|---|---|---|
| Display: Banner Mobile web, Desktop, CTV |
Count-on-download (COD) | Begin-to-render (BTR) |
| Display: Non-banner (such as Native and Interstitial) |
BTR compliant | |
| App | 1-pixel (BTR compliant) | |
| Video | 1st frame (BTR compliant) | |
Benefits of begin-to-render for display ads
The switch to BTR provides the following benefits:
- BTR is the industry standard and preferred methodology for impression counting.
- BTR streamlines publisher workflows, such as eliminating the need to buffer your COD campaigns to deliver against BTR terms.
- BTR aligns impression measurement methodologies with demand-side platforms.
Timeline for the change
February 17, 2027: Ad Manager and AdSense impression measurement will shift from count-on-download (COD) to begin-to-render (BTR) for display inventory on web, mobile web, and CTV banner. No action is required.
Preparing for the change
When determining an impression, begin-to-render serves as a more rigorous measurement standard than count-on-download. COD counts ads that have loaded to a page but were potentially abandoned before fully rendering, such as if a user quickly navigates away. Therefore, following the shift, you may notice a decrease in total display impressions, as BTR counts an impression later in the ad serving process.
To better prepare for this change, review the following options.
Run a report to estimate impact
Ad Manager publishers can estimate the potential difference between their current COD and future BTR impressions by reviewing their existing web display versus rendered metrics in reporting. To get a clearer understanding of how your metrics may adjust, you can report on your current count-on-download and begin-to-render impressions and calculate the difference.
For example, here’s one way you can generate a report on the potential impact:
- Sign in to Google Ad Manager.
- Click Reporting, then Interactive reports.
- Click Create my own report.
- Enter a report name, and make other setup selections (such as the date range) as desired.
Note: We advise running a historical report with a start date after August 12, 2026. - Add the following dimensions:
- Demand channel
- Inventory format
- Inventory type (expanded)
- Device category
- Add the following metrics:
- Ad server impressions
- Ad server begin to render impressions
- Additional metrics coming soon: "Ad Exchange begin to render impressions," "Yield group begin to render impressions," "Total begin to render impressions."
The estimated decrease in impressions for the publisher is calculated as the difference between Ad server (or Ad Exchange / Yield group) impressions (using the count-on-download method until February 17, 2027) and Ad server (or Ad Exchange / Yield group) begin-to-render impressions. After February 17, 2027, and a brief ramp-up of traffic, Ad server (or Ad Exchange / Yield group) impressions will align with Ad server (or Ad Exchange / Yield group) begin-to-render impressions.
Review discrepancies
In addition to Ad Manager reporting, you can review discrepancy reports you have with buyers or third-party measurement providers. The change in impression counting methodology is designed to reduce discrepancies with the impressions counted by your advertiser partners and third-party measurement providers.
Best practices
Creative optimization
You should always optimize your creatives to improve asset downloading and rendering on your sites. Learn more about creative optimization. Chrome will disable ads that consume too much network / CPU usage (as explained in Heavy ad criteria), which may lead to issues with creative downloads and an inability to render creative assets.
Lazy Loading and Lazy Rendering
Lazy loading settings impact impression measurement for both COD and BTR methodologies. Lazy rendering directly affects BTR measurement because it affects when creative assets start rendering in the user’s browser. Raising renderMarginPercent or fetchMarginPercent causes assets to render earlier in the user experience. Note that these settings also increase resource demands on your network and the end-user’s device, so consider all trade-offs before adjusting them. Learn more about ads best practices.
About impression counting and MRC accreditation
The Interactive Advertising Bureau (IAB) and the Media Rating Council (MRC) in partnership with other industry bodies, periodically review and update industry standards for impression measurement. They recommend guidelines to standardize how impressions are counted across formats and platforms. Over time, the standards for counting an ad impression on the web have evolved from counting an impression when the ad is served to counting an impression when the ad starts to download on the user’s device (that is, the ad begins to load on a page), and now to counting an impression when the creative has successfully loaded and started to render its assets on the user’s device.
The definitions are summarized below:
- Served impression: An impression is counted when an ad is sent (or "served") to a publisher by the ad server. The ad creative may or may not be downloaded to the user’s device, rendered, or viewed by the user.
- Downloaded impression: An impression is counted only when the ad server responds to a request, and the creative asset begins to download to the user's device.
- Begin-to-render (BTR): An impression is counted when the ad creative has successfully loaded and begins to render on the user’s device.
Ad Manager will continue to retain accreditation for Display, Video, and Rich Media creatives within Desktop, Mobile Web, and Mobile application environments. To learn more, visit Description of methodology.