Low Fill Rate

Why ad slots are empty more than expected — missing ads.txt, low consent rates, Tier-3 geo traffic, narrow ad sizes, high price floors, and IVT-suppressed demand partners.

A low fill rate means your ad slots are loading but not always serving a paid creative. Some unfilled impressions are normal — not every visitor in every market generates a winning bid. This article covers the common causes and fixes.

What is a normal fill rate?

For a well-configured site with broad, quality traffic:

Banner slots on US/UK/Western European traffic: 70–95% fill rate
Banner slots on Tier-2/3 geo traffic: 40–70% fill rate
Video slots: typically lower than banner due to fewer video-capable buyers

If your fill rate is significantly below these ranges, one of the issues below is likely the cause.

Common causes

1. Missing or incorrect ads.txt

DSPs that verify your inventory through ads.txt will not bid if the file is missing or does not include the correct entry for Advlume. This is the most common cause of low fill on an otherwise healthy site. See ads.txt Setup Guide.

2. Low consent rate (EEA traffic)

Non-consented impressions have a much smaller pool of eligible buyers. If most of your traffic is from the EEA and your consent rate is low (below 50%), fill will be poor for those sessions. Work on improving your consent banner presentation.

3. Audience geography

Traffic from Tier-3 geos (Southeast Asia, Sub-Saharan Africa, most of Latin America) has fewer active advertiser campaigns bidding on programmatic inventory. This is expected and structural — it will not be fixed by technical changes.

4. Ad sizes with limited demand

If your slots only include unusual sizes (e.g. 468×60 only), the pool of eligible buyers is smaller. Always include 300×250 as a fallback — it has the deepest demand pool of any banner size.

5. Price floor too high

If a floor price is configured for a slot that is above what demand partners are willing to pay for that inventory, impressions will remain unfilled. Contact your account manager if you believe your floors may be misconfigured.

6. IVT-suppressed demand

If a DSP has independently detected high IVT on your domain, it may have suppressed its bids. Check the bidder breakdown in your Revenue Report — if a partner that was previously active has dropped to near-zero bids, this may be the cause.

Improving fill rate

Ensure ads.txt is correct and up to date.
Enable as many ad sizes as your layout allows per slot.
Ensure all demand partners are enabled in your site settings.
Improve consent rates for EEA visitors.
Reduce IVT rates if elevated (see Avoiding IVT on Your Site).