You can't judge without understanding "why the numbers are different"

The same question recurring in almost every organization that runs advertising: While the ad platform reports very high conversion rates, GA4 shows significantly lower or even completely different conversion rates. Especially for meta (Instagram) ads, the discrepancy between conversion performance shown in Ads Manager and actual website purchase performance can be incredibly confusing for clients. This confusion stems not from a flaw in the tool itself, but from a difference in how the data is interpreted.

Fundamental Differences in Purpose between Advertising Data and Web Analytics Data

While advertising data and web analytics data share the same term, "conversion," their original design purposes differ. Advertising platform data exists to demonstrate and optimize ad performance. Web analytics data, like GA4, exists to objectively record actual user behavior on a site. This difference in purpose is the starting point of all data differences.

How Advertising Platforms Track Data

Advertising platforms fundamentally collect data based on attribution. They link the time a user sees an ad, clicks on it, and subsequent actions within a certain period of time to ad performance. Conversion data from advertising platforms has the following characteristics.

• Not only clicks but also views can be included in conversion attribution.
• Actions that occur within a certain period of time are considered to be the result of the advertising effect.
• The higher the ad performance is judged, the more advantageous it is for automatic bidding and budget execution.

In other words, the advertising platform collects data with the goal of asking, “How influential was this advertisement?”

How GA4 Tracks Data

GA4 records data based on actual events occurring on a website, not advertising performance. Page views, scrolls, clicks, and purchase completions are only recorded when actual user actions occur. GA4 data features include the following:

• Only actual visits and event occurrences are recorded.
• Ad exposure alone does not count as a conversion.
• It is relatively conservatively calculated based on cookies, sessions, and events.

GA4 is a tool that shows what actually happened on your site, not just what “ads likely contributed.”

Why Ad Conversion Rates and GA4 Conversion Rates Differ

The reason these two data sets differ is simple: they view the same behavior based on different criteria. Advertising platforms define conversions from an ad-centric perspective, while GA4 defines conversions based on user behavior. The main reasons for this discrepancy are as follows:

• Whether conversions after ad exposure are included in ad performance
• The time span between the click and conversion points
• Differences in how duplicate counting of identical users is handled
• Data loss due to browser, device, and tracking restrictions

This difference is not an error, but rather a result of each tool functioning properly for its own purpose.

In particular, the reason why Instagram ad conversion rates are always high

The primary reason meta ads appear to have particularly high conversion rates is view-through attribution. Even if a user doesn't click on the ad, meta ads can attribute a purchase within a certain period of time after viewing the ad to the ad's performance. This structure results in the following:

• Actual purchases occur through searches, direct visits, and repeat visits.
• Meta determines that “ad exposure influenced purchases.”
• In Ads Manager, the conversion rate appears to be high.

However, GA4 often records these purchases as direct traffic or conversions from other channels. In these cases, GA4's purchase conversion rate often more closely reflects actual performance.

So what data should we base our judgment on?

The answer is not to select one data, but to divide the criteria according to the role.

Advertising data is appropriate for the following decisions:

• Comparison of advertising materials
• Compare performance across campaigns
• Determining the direction of advertising algorithm optimization

GA4 data should be the basis for the following decisions:

• Actual purchase conversion rate
• Whether to improve the site UX
• Actual contribution by inflow channel

You need to use advertising platform data to determine "how to run your ads," and GA4 data to determine "whether your business is actually growing."

The most dangerous interpretation

The most common and dangerous mistake is interpreting an advertising platform's conversion rate directly as business performance. While this approach may look good in short-term reports, it can lead to increased advertising costs and an illusion of performance in the long run. The following interpretations, in particular, require caution.

• The simple connection between increased ad conversion rates and increased sales.
• Attempts to align GA4 figures with advertising platform figures
• The attitude of attributing fundamental differences in data to mere “tracking errors”

Insight Summary

Advertising data and web analytics data are not competing tools, but rather serve different purposes. Advertising data demonstrates the potential contribution of an ad, while GA4 reveals actual user behavior. The apparent high conversion rate of meta ads is a result of the structural attribution calculation method, and it's reasonable to base actual purchase performance on web analytics data like GA4. The key is not to match the numbers in each metric exactly, but to accurately understand what each piece of data is telling us.