You open GA4 and see 40 purchases. You open Google Ads and see 63. Same store, same week, same campaigns. One of them is lying to you, and you have a meeting in twenty minutes.

Here is the uncomfortable truth. Both numbers are probably correct. They are just answering different questions.

The four reasons the numbers split

1. They attribute to different moments in time

Google Ads reports a conversion on the day of the click. GA4 reports it on the day of the conversion.

So someone clicks your ad on Monday and buys on Thursday. Google Ads books that sale on Monday. GA4 books it on Thursday. Look at a single week and the two reports slide past each other like badly aligned wallpaper.

This one reason alone explains most of the gaps people panic about.

2. Google Ads counts conversions GA4 cannot see

Google Ads uses modelled conversions. When a user does not consent to cookies, or their browser blocks the identifier, Google estimates what probably happened based on similar traffic it can measure.

GA4 does some modelling too, but far less aggressively in standard reports. So Google Ads fills in gaps that GA4 leaves empty.

3. They disagree about who gets credit

Google Ads gives credit to the Google Ads click. That is its whole job.

GA4 uses data driven attribution across every channel. If a customer clicked your ad, then came back through an email, then bought, GA4 might hand most of that credit to email. Google Ads still counts the whole sale as its own.

Neither is wrong. They are keeping different books.

4. Different conversion windows

Google Ads defaults to a 30 day click window and you can stretch it to 90. GA4 has its own lookback settings. If nobody has checked these in a year, they almost certainly do not match.

So which number should you trust?

Use Google Ads numbers to make Google Ads decisions. Bidding, budgets, pausing campaigns. That is the data the algorithm actually optimises on, so arguing with it is pointless.

Use GA4 to understand the customer journey. Which channels assist, where people drop off, what the path to purchase looks like.

Use your actual sales system, Shopify or your CRM, as the source of truth for revenue. Neither ad platform knows about refunds, failed payments, or the order your sales team cancelled on Friday.

When the gap is genuinely a problem

Some variation is normal and healthy. Roughly 10 to 20 percent between GA4 and Google Ads is business as usual.

Start worrying when you see any of these:

• The gap is above 30 percent and stays there across several weeks.

• GA4 shows dramatically more conversions than Google Ads. This usually means duplicate event firing in GA4 rather than a Google Ads problem.

• One platform drops to near zero overnight. That is not attribution. That is something broken.

• Neither platform matches Shopify or your CRM by a wide margin. If both are wrong in the same direction, the problem is upstream of both.

How to actually check it, in about fifteen minutes

1. Compare the same window, properly. In GA4, set the report to use the Google Ads click date rather than the event date, or simply compare a full month instead of a week. Short windows exaggerate the timing gap.

2. Check for duplicate events. In GA4 realtime, complete one test purchase and watch the event count. You should see exactly one purchase. If you see two, you have found your problem.

3. Compare against Shopify or your CRM. Pull the real order count for the month. That tells you which platform is closer to reality.

4. Check the conversion windows. Google Ads conversion settings, then GA4 attribution settings. Write both down.

5. Check what is actually marked as a conversion. A surprising number of accounts count add to cart, newsletter signups, and purchases all together, then wonder why the number looks inflated.

The mistake almost everyone makes

People try to force the two numbers to match. They spend weeks adjusting settings, chasing a perfect alignment that is not technically possible.

The goal is not identical numbers. The goal is a stable, explainable gap. If you can say “Google Ads runs about 18 percent higher because of click date attribution and modelling”, your tracking is healthy. If the gap swings from 5 percent to 60 percent month to month, something really is broken.

Quick reference

• Gap under 20 percent, stable: normal, leave it alone.

• Gap 20 to 30 percent: worth a look at attribution settings and conversion windows.

• Gap over 30 percent, or unstable: something is misconfigured or double firing.

• Either platform far off your real orders: start with the data layer and the tags, not the reports.

Need this fixed properly?

If your numbers have drifted far enough apart that you no longer trust either one, that is fixable and usually faster than people expect. I set up and repair tracking for ecommerce stores and lead generation businesses, so the numbers in your ad accounts match the money in your bank account.

Have a look at what I do, or book a call and we can go through your setup together.