How to troubleshoot sharp CPM drops?

Ad Optimization
Last updated: September 15, 2021 | by Kean Graham
How to troubleshoot sharp CPM drops

This post was most recently updated on September 15th, 2021

Every publisher values his site’s content and metrics. Whether it’s an impressive low bounce rate or a high ad viewability score, publishers always try to keep site metrics on an upward trend.

That’s why it’s crucial that any sharp drops or spikes in performance are dealt with right away, especially when it comes to CPMs.

Let’s take a closer look at what can cause sharp CPM drops and how to troubleshoot them.

How to troubleshoot sharp CPM drops? MonitizeMore

Seasonal traffic

No two websites are alike when it comes to content, audience, and site metrics. That’s why it’s important to know if your site’s content is geared towards audiences that have specific viewing habits.

For example, a site that sells Super Bowl tickets would most likely see traffic coming in in bulk 2-4 weeks before the first Sunday of February.

In the same manner, an international site that sells Independence Day memorabilia would see spikes in traffic from different countries on different days leading to each country’s Independence Day.

For example, there could be a spike of Brazilian traffic on days leading up to Sept 7 while on days leading to May 20, it could be Cuban traffic.

Case in point, the content of the site is what drives these visitors, and the influx of a non-standardized set of visitors (especially non-tier 1) is simple enough to drop CPMs.

Troubleshooting: Investigate year on year traffic data and compare monthly impressions as well as geographical data. If you find that there are months where your site’s visitors are focused on a specific country, or there is merely a spike, you might be subject to seasonal traffic.

Bot traffic

Non-human traffic is very risky to be involved in. With such a practice, not only will your CPMs drop (because impressions are invalidated) but your site would also be subject to blacklisting from managed demand and header bidding partners.

Troubleshooting: With the advancements in technology these days, it is often hard to spot bot traffic as they utilize varying IPs, proxies, clone legitimate MAC addresses and use other forms of spoofing. The best way to prevent this is to have fraud traffic suppression technology in place.

Buying cycles

Advertisers rely on data to decide how, when, and where they are going to spend their budget. It usually occurs at two regular intervals. First, there is the quarterly buying cycle wherein spending for the past quarter is analyzed and acted upon.

This means that for the first few days of the next quarter, buying is set to minimal. The second buying cycle is the yearly one wherein the past year is analyzed. In this instance, it is January that is adversely affected.

Troubleshooting: Similar to how you troubleshoot seasonal traffic, investigate your monthly data over a couple of years and see if January CPMs do drop. Also check to see if there is a drop at the start of each quarter (April, July, and October).

Policy changes

Regardless of whether your site obtains traffic via arbitrage or SEO, policy changes from your traffic sources can impact your reach and thus affect your CPMs.

For example, the recent GDPR is sure to impact publishers that have heavy EU traffic and have not yet implemented a consent solution.

Likewise, the previously alarming Facebook News Feed change also impacted large publishers that heavily relied on their content being shared by pages and influencers.

Troubleshooting: Always stay on top of ad tech-related news. If there are algorithm changes that may affect how your site receives traffic or limits your monetization capabilities, it will surely affect CPM too.

Value CPM

If you are using DFP, the value CPM is essential for price priority line items and should be updated regularly. Why? This is because if there is a discrepancy on DFP and the UI of the ad network, it is your CPM that is going to be affected.

For example, on a particular day, you had a line item running at $1.50 value CPM, and it got 5,000 impressions for total revenue of $7.5. On the UI, on the other hand, it showed that it only reached 4,750 impressions that gave you $6.8.

Calculating the value CPM, $6.8 (UI rev) divided by 5,000 (DFP impressions) x 1000, you’re looking at a CPM of only $1.36 which is a loss for you especially if you have numerous orders that could easily beat $1.36 CPM.

Troubleshooting: Regularly monitor your price priority line items and make sure that they have accurate value CPMs.

Ad configuration errors

CPM drops may also occur if there are inconsistencies with your ad setup]. For example, if you meant to replace a 300×250 Ad Exchange ad with a 300×600 on your desktop sidebar and mistakenly encoded 300×60 only, that is sure to cause a drop in CPMs right away.

Another example is deploying a 728×90 ad on mobile, by mistake, instead of on the desktop. While those are inevitably going to look cropped and ruin your user experience, the bigger issue here is that most advertisers know there is no 728×90 on mobile. Thus, you’ll only get a few bids and ruin your CPM.

Troubleshooting: Be sure you know how to run granular reports on whatever portal you are using (DFP, Managed Demand, Header Bidding). Seeing an inconsistency and correcting it right away is vital.

Technology malfunction

Similar to configuration errors, it is also possible that some of the technology in the whole exchange could malfunction. Some examples could be:

  • Ad inserter plugin or code crashes
  • Parent theme removed a specific div that housed your ad unit
  • The creative server of demand source crashed
  • Updated ad tags were deployed rendering current ones obsolete
  • DDNS communication issues

One piece of technology that is worth noting is the HTTP vs. HTTPS issue. Some browsers are picky and only display creatives on sites that have uniform content, i.e., if your site is HTTP and is loading an HTTPS creative, the creative is suppressed.

Troubleshooting: You should be able to pinpoint where the bottleneck is right away (your hosting, DFP, 3rd party issues, etc.) by doing routine checks on the various reporting portals at your disposal.

If you have a developer team, they should also have the capability to report on publisher-side malfunctions.


Seeing sharp CPM drops is a publisher’s worst nightmare. We can help you troubleshoot and identify the issue as well as help prevent this from happening in the future. MonetizeMore is a Google Certified Publisher Partner and experts at tackling these sharp CPM drops. Want us to help solve your CPM drops and optimize your ad inventory? Sign up for a Professional account at MonetizeMore today!

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