While third-party cookies are here to stay—for now—marketers can’t afford to be complacent about measurement. With privacy regulations mounting and most consumers blocking cookies, measuring digital ad performance remains a complex and challenging task.

Here are three key challenges marketers face, despite third-party cookies remaining part of the equation.

1. Most consumers are already untrackable—even in a cookie-enabled world

While Google Chrome allows third-party cookie tracking, it’s the exception, not the rule. Both Safari and Firefox block third-party cookies by default. Plus, many users opt out using tools like Global Privacy Control, which lets users communicate their privacy preferences to websites.

• 77.1% of US consumers have used at least one privacy tool, according to EMARKETER’s July 2024 “US Consumer Attitudes on Advertising and Privacy” survey.
• Additionally, nearly half (45.9%) of consumers sometimes or rarely accept cookie access when prompted, according to the same survey.

2. Digital ad measurement is increasingly fragmented across channels

As marketers combat signal loss, they’re turning to channels less reliant on cross-site or cross-app tracking, according to EMARKETER’s “Ad Measurement Trends H2 2024” report.

• 76% of brand and agency marketers worldwide plan to increase their digital ad spend on social media/influencer marketing in 2025, while 64% will increase retail media spend and 47% will increase spend on connected TV (CTV), according to October 2024 data from Digiday and NCSolutions.
• All these channels benefit from “large logged-in audiences,” wrote analyst Evelyn Mitchell-Wolf in the EMARKETER report.

However, stitching together data from multiple channels can be difficult.

“Platforms often limit access to user-level ad performance or delivery data due to their own financial interests or legal requirements regarding privacy, the latter of which are mounting by the quarter,” wrote Mitchell-Wolf. “Even when user-level data is available, metrics from one platform are rarely easily compared with metrics from another.”

3. US privacy laws are forcing marketers to abandon legacy measurement methods

As of April 2025, 19 states have enacted comprehensive privacy laws, with many more active in legislation, according to the International Association of Privacy Professionals (IAPP).

• These laws, including the California Privacy Rights Act (CPRA) and the Colorado Privacy Act (CPA), dictate when, how, and with whom advertisers can sell and share consumer data—regardless of cookie availability.
• Depending on where a company operates, it may have to follow a number of different rules to stay in compliance.

As a result, 38% of US advertising professionals have made some adjustments to their measurement strategy, while 14% say they’ve significantly changed their approach, according to July 2024 data from Comscore Inc. and Proximic.

The bottom line: Despite Google’s pivot on cookies, marketers must develop holistic, privacy-first measurement strategies. They can do this by:

• Boosting zero- and first-party data collection efforts.
• Leveraging data clean rooms for secure, privacy-compliant data matching.
• Experimenting with incrementality testing and marketing mix modeling (MMM) for a more accurate picture of ROI and campaign performance.

This was originally featured in the EMARKETER Daily newsletter. For more marketing insights, statistics, and trends, subscribe here.