Understand why Meta Ads and Google Ads report different conversion numbers and which platform to trust for attribution.
• Different attribution windows: Google uses 30-day click (default) vs Meta's 7-day click
• Both over-attribute: 10-40% overlap is normal when running both platforms
• iOS 14+ impact: Meta lost 20-40% tracking, Google lost 10-20%
• Source of truth: Always use Shopify revenue for reconciliation, not platform-reported numbers
| Feature | Meta Ads | Google Ads | Winner |
|---|---|---|---|
| Attribution Model | 7-day click, 1-day view (default) | 30-day click, 1-day view (default) | |
| View-Through Attribution | Included by default (1-day window) | Included by default (1-day window) | Tie |
| Conversion Tracking | Pixel + CAPI (server-side) | Google Tag + Enhanced Conversions | Meta |
| iOS 14+ Impact | 20-40% conversion loss | 10-20% conversion loss | |
| Attribution Overlap | 25-35% typical overlap | 20-30% typical overlap | Tie |
| Reporting Delay | Up to 3 days for full attribution | Up to 2 days for full attribution | |
| Cross-Device Tracking | Limited after iOS 14 | Better with Google account login | |
| De-duplication | No automatic de-duplication | No automatic de-duplication | Tie |
Google's longer attribution window captures more delayed conversions, especially for higher-consideration purchases
Both platforms include VTA, which inflates ROAS. Consider using click-only attribution for more conservative measurement
Meta's CAPI is more mature and easier to implement, especially with Shopify's native integration
Google Search is less affected by iOS ATT since users actively search for brands. Meta's prospecting campaigns were hit hardest
Both platforms over-attribute conversions. Use Shopify revenue as source of truth and expect 10-40% total overlap
Google's reporting stabilizes faster, but both platforms need 48-72 hours for accurate conversion data
Google can track users across devices when they're logged into Google accounts. Meta's cross-device tracking was severely impacted by iOS ATT
Neither platform de-duplicates with other ad platforms. You must manually reconcile using Shopify data
Shopify revenue is the only reliable number. Meta and Google will both over-report due to attribution overlap and view-through conversions. Trust hierarchy: Shopify > GA4 > Ad Platforms.
If Meta reports €10,000 in revenue and Google reports €8,000, your actual Shopify revenue might be €12,000-14,000. Both platforms claim credit for the same conversions using last-click attribution.
Blended ROAS = Total Shopify Revenue ÷ (Meta Spend + Google Spend). This is your true marketing efficiency, not the inflated platform-reported ROAS.
Set both platforms to the same attribution window (7-day click recommended) for more accurate comparison. Longer windows capture more conversions but increase overlap.
Use Meta CAPI and Google Enhanced Conversions to recover 10-20% of conversions lost to iOS 14+ restrictions. Shopify offers free native CAPI integration.