Why Google Ads and GA4 Show Different Conversion Numbers

The Mismatch Every Marketer Has Seen

You pull your monthly report. Google Ads says 85 conversions. GA4 says 62. Your CRM shows 100 actual sales.

Three Google products. Three different numbers. And your CFO wants to know which one to believe before approving next quarter's budget. None of them match your actual sales.

This isn't a tracking error. It's three systems measuring the same thing in three different ways.

The 5 Reasons They Never Match

1. Different Attribution Models

Google Ads uses its own attribution model, optimised for showing ad performance in the best possible light. It credits conversions to the ad click, even if the user interacted with 10 other channels between clicking the ad and converting. Independent analysis of 792 marketing models found Google Ads over-reports by a median of 18% compared to modelled incrementality (Cassandra, 2025).

GA4 uses Data-Driven Attribution across all channels. It distributes credit between Google Ads, organic search, social, email, direct — everything it can see. Your Google Ads conversions get diluted because GA4 is sharing credit with other channels.

Same user, same conversion. Google Ads gives the ad 100% credit. GA4 might give it 35%.

2. Different Counting Methods

If a user clicks your ad once and makes two purchases, Google Ads counts two conversions by default. GA4's counting depends on how you configured the conversion event.

Check: Google Ads → Conversions → Settings → Count. If it says "Every" and your GA4 conversion counts "One per session," there's your gap.

3. Different Attribution Windows

Google Ads counts view-through conversions by default — someone saw your ad but didn't click, then converted within 1 day. GA4 generally doesn't count these. That's a one-directional gap: Google Ads will always count these extra conversions that GA4 doesn't see.

4. Consent Mode & Ad Blockers

This is the silent discrepancy source that's growing fast.

Google Ads uses conversion modelling to estimate conversions from users who declined tracking consent. If 30% of your users decline cookies, Google Ads models those missing conversions and adds them to your total.

GA4 in default mode doesn't model unconsented conversions. If a user blocks tracking, GA4 simply doesn't see them.

Result: Google Ads reports conversions for users that GA4 never knew existed.

With iOS 26 stripping click IDs and Safari capping JS cookies at 7 days, this gap is widening. Google Ads' modelling fills in what it can't see. GA4 just has a hole.

5. Data Processing Timing

GA4 has a 24-72 hour processing delay and conversion data can update for up to 7 days. Google Ads is near-real-time. Wait 3-5 days into the new month before comparing.

What's "Normal" vs. What's Broken

The Audit Checklist

If you're above 25%, check these in order:

1. Counting method. Google Ads → Conversions → does it say "Every" or "One"? Match to your GA4 configuration.
2. Attribution window. Google Ads → Conversions → click-through window. Set to same period as your GA4 property attribution settings.
3. View-through. Google Ads → Conversions → include view-through conversions? If yes, that's conversions GA4 will never count.
4. Consent mode. Is Google Ads modelling consented conversions while GA4 isn't? Check both implementations.
5. Tag firing. Use Google Tag Assistant to verify both GA4 and Google Ads tags fire on every page, including post-conversion pages.
6. Cross-domain. If your checkout is on a different domain, verify GA4 cross-domain tracking is configured. Google Ads conversion tag doesn't need this — it tracks at the click level.

Which Number to Trust (For What)

None of them are "right" in an absolute sense. Each serves a different purpose.

The dangerous mistake is using Google Ads data for cross-channel budget allocation. Google Ads data tells you how Google Ads is performing according to Google. That's useful for Google Ads. It's not useful for deciding whether to shift budget to Meta.

When the Discrepancy Is Actually Useful

The gap between Google Ads and GA4 actually tells you something useful.

If Google Ads reports 85 and GA4 reports 40 for the same campaign, that means GA4 is giving 45 of those conversions to other channels. Those channels contributed to the conversion journey, and Google Ads was just the last (or one of many) touchpoints.

The bigger the gap, the more Google Ads is overclaiming. A large gap on a particular campaign suggests that campaign captures existing demand rather than creating it.

A small gap suggests the campaign drives genuinely incremental conversions that other channels didn't contribute to.

This is crude, but it's directional signal you already have in your data.

Related Reading

• Why Your Platform Reports Don't Match — the broader problem across all platforms, not just Google
• How Much Are Your Ad Platforms Over-Reporting? — the data on platform inflation (Meta: 134%, Google: 18%)
• Why Did GA4 Remove Most Attribution Models? — what changed in GA4's attribution and why

Holly Henderson

Co-Founder, mbuzz

Holly Henderson is Co-Founder of mbuzz. With 10+ years in marketing including roles at Westpac, Avon, and Forebrite, she's obsessed with making measurement actually useful.

Harvard Extension School Forebrite Westpac Avon