Why Your Fill Rate Is Low and How to Fix It Fast
When your fill rate drops, you’re not just losing impressions you’re leaving money on the table. Every percentage point you’re missing could mean hundreds (or thousands) in lost revenue this month.
Let’s fix that
You’ve probably heard the usual stuff:
- Just add more demand partners
- Optimize your floor prices
- Try lazy loading
But here’s the truth those are surface level fixes.
For publishers already making $2K+/month, the real issues are under the hood in timeouts, SDK settings, invalid traffic filters, and bid logic most people never touch.
If you’re looking for a foundational overview of common fill rate issues in Google AdExchange, check out our post on “Top Reasons for Low Fill Rate Issues in Google AdExchange“.
The steps below go beyond the basics they’re meant for publishers already running programmatic at scale and looking to solve deeper technical bottlenecks.
Let’s walk through the actual things hurting your fill rate and how to fix them this week.
1. Your Timeout Setting Is Too Short for Your Bidders
Example:
You’ve got Prebid set to timeout at 800ms, but some of your best paying demand partners consistently return bids at 1.2–1.5s.
Result? Their bids never make it to the auction. You lose the fill and the CPM.
Fix:
➡️ Increase your Prebid or header bidding timeout to 1200–1500ms, depending on your average network latency.
Where to check:
- Prebid config file (setConfig { timeout: 1500 })
- GAM delivery diagnostics
- Chrome DevTools → Network tab → measure bid response times
2. Your SDKs Aren’t All Talking to Each Other
Example:
Your app uses Google Mobile Ads SDK, but you also added a third-party SDK for mediation. They’re not in sync some impressions time out or error out completely.
Fix:
➡️ Update all SDKs to the latest versions.
➡️ Make sure mediation chains are properly ordered and using fallback logic.
Where to check:
- Android/iOS logcat logs
- Your mediation platform
- Crashlytics or error monitoring tools
3. Your Ad Unit Sizes Don’t Match Demand Expectations
Example:
You’re serving 300×250 units in a layout labeled as “responsive,” but the ad call renders them in a 600px-wide container. Many DSPs reject mismatched size impressions, especially on mobile.
Fix:
➡️ Make sure your ad slots match exactly the size of the actual container and declared size in the ad request.
➡️ Use data-ad-sizes properly if you’re using GPT.
Where to check:
- Chrome DevTools → Inspect element
- Google Publisher Console (?google_console=1)
- Ad unit settings in Google Ad Manager
4. You’re Sending Low Quality or Invalid Traffic (Without Knowing)
Example:
You bought cheap traffic from an aggregator or your audience skews too heavily toward one GEO. DSPs detect this as non-converting or suspicious traffic. They stop bidding.
Fix:
➡️ Run your domain through traffic quality tools (like IAS, Pixalate, or HUMAN).
➡️ Segment traffic by source and block low-quality referrers in GAM or via SSP rules.
Where to check:
- SSP dashboards
- GAM reports by traffic source/referrer
- 3rd-party verification platforms
5. Your Line Item Priorities Are Misconfigured in GAM
Example:
You’ve got programmatic demand running at priority 12, but remnant house ads are set at priority 10. GAM fills with house ads before paid demand even has a shot.
Fix:
➡️ Double-check all line item priorities.
➡️ Paid demand (especially AdX or Open Bidding) should run at priority 12 or 13, not below house ads.
Where to check:
- Google Ad Manager → Delivery → Line Items → Priority column
For a full breakdown of how to configure and prioritize Ad Exchange demand correctly, refer to Google’s guide on Best practices for Ad Exchange line items.
6. You’re Using Outdated Formats That Buyers Don’t Want
Example:
You’re still using banner-only ad units. Some DSPs are shifting spend to native, rich media, or video inventory and deprioritize basic banners.
Fix:
➡️ Test adding native or video ad units where appropriate.
➡️ Make sure the creatives are loading properly and the placements are viewable.
Where to check:
- GAM Ad Unit settings
- Active creative types per SSP
Quick Action Checklist for Fixing Your Fill Rate This Week
- Increase your header bidding timeout to 1200–1500ms.
- Update SDKs across your app or site to ensure they’re all compatible.
- Verify your ad unit sizes match the container sizes and declared request sizes.
- Run a traffic quality audit using tools like IAS or Pixalate.
- Check and adjust line item priorities in Google Ad Manager.
- Add new ad formats like native or video to expand your demand pool.
Need Help?
If you’re struggling to get your fill rate where it needs to be, consider a free audit from MagicBid. Contact us today at support@magicbid.ai We can help you identify the issues specific to your setup and provide actionable recommendations.
Fixing your fill rate isn’t a one-size-fits-all process, but with these specific actions, you should see a difference this week. Time to stop leaving money on the table and start optimizing for more revenue.
How MagicBid Helps You Earn More
If you’re not making the most of your ad space, you’re leaving money on the table.
MagicBid helps web, app, and CTV publishers maximize revenue with smarter ad placement and optimization tools.
- Web Monetization: Get better ad visibility, higher engagement, and more revenue from every impression.
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With MagicBid’s advanced ad tech and expert support, you can turn your traffic into higher earnings without the guesswork.
Connect with us now to get a free ad revenue evaluation.