GA4 says 100 conversions and Google Ads says 150. Neither platform is lying; they are answering different questions, and they are built to report different numbers on purpose.

Most explanations stop at why the numbers differ. I’ll cover that, but the part that matters more is which number to trust for which decision.

Google Ads measures its own influence. It only sees the clicks and impressions within its own ecosystem, which makes sense given that it is optimizing for Google Ads performance. GA4 tries to measure everything across channels and touchpoints, the whole customer journey, but it is also missing data constantly because of blocked cookies, denied consent, and cross-device gaps when User-ID isn’t set up. So a 20-30% discrepancy between the two is normal and built in.

Why do the numbers differ?

There are five main reasons;

  1. Attribution windows. Google Ads defaults to 30-day click and 1-day view-through, while GA4 defaults to 90 days. If the sales cycle is 60 days and Google Ads is running 30-day windows, it’s missing conversions.
  2. Conversion counting. GA4 counts every conversion instance by default, so a customer who buys three times is three conversions. Google Ads lets you choose between counting one or counting all, and if those settings don’t match, neither will the numbers.
  3. Click date vs conversion date. This is the one that confuses stakeholders most. Google Ads reports a conversion on the date of the click, and GA4 reports it on the date of the conversion. If someone clicks on May 1 and converts on May 5, Google Ads says May 1 and GA4 says May 5. Both are correct.
  4. Cross-device tracking. Google Ads uses Google Signals automatically, so anyone logged into a Google product gets tracked across devices. GA4 needs User-ID set up to do the same thing, and without it GA4 sees device A and device B as two different people.
  5. Modeled conversions. When cookies are blocked or consent is denied, both platforms model what they can’t observe. Google Ads applies additional modeling on top of what GA4 exports, and more modeling means higher numbers.

Which number do I use for which decision?

Google Ads tells you how Google Ads is performing, and GA4 tries to tell you how everything is performing. My opinion;

  • Google Ads numbers for campaign optimization and bidding decisions, evaluating Google Ads ROAS specifically, and anything where you’re optimizing within Google Ads and need the platform’s data-driven attribution to improve performance.
  • GA4 numbers for cross-channel budget allocation, understanding the full customer journey, board or executive reporting on total attribution, and any time you need a ‘neutral’ view that doesn’t favor a single platform.

How do I explain it to a stakeholder?

When a CMO asks why Google Ads says 150 conversions but GA4 says 100, a short answer is usually enough:

“Google Ads counts conversions on the click date and only tracks its own ecosystem. GA4 counts on conversion date and tries to track everything. A 20-30% gap is normal. We use Google Ads data to optimize our ad spend and GA4 data to see the full picture across all channels.”

If they push back, the click date vs conversion date example usually lands: “If someone clicked our ad on the 1st and bought on the 5th, Google Ads records that sale on the 1st. GA4 records it on the 5th. Same sale, different reporting logic.”

What can I do about it?

The numbers won’t match by design, so I’d stop trying to make them. A few things are still worth checking;

  • Align attribution windows across platforms where possible. If the sales cycle is 60 days, don’t run 30-day windows anywhere.
  • Check the conversion counting settings so that “count one” vs “count every” is intentional.
  • Wait 48+ hours before comparing, since GA4 has processing lag that Google Ads doesn’t.
  • Use each platform for its strength: Google Ads for optimizing Google Ads, GA4 for the cross-channel view.

The platforms are never going to agree because they’re measuring different things for different purposes, and chasing a perfect match is wasted effort. What matters is knowing which number answers the question being asked, so Google Ads numbers for Google Ads decisions and GA4 numbers for cross-channel ones.