Google’s September GSC Impression Drop Explained: What Really Happened (and How to Fix It)

Google’s September GSC Impression Drop Explained: What Really Happened (and How to Fix It)

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Did you notice a sudden, massive drop in your Google Search Console (GSC) impressions recently? Don’t worry, you aren’t alone!

According to an SEO expert, Tyler Gargula, almost 87.7% of sites experienced drops in impressions in mid-September 2025 after Google disabled the &num=100 parameter and made other significant changes.

But here’s the reality: many of those drops are likely not caused by lost rankings, algorithmic penalties, or sudden demand shifts. Instead, they look like measurement shifts, data cleanup, and structural changes in how Google reports visibility.

This blog specifically focuses on the explicit reasons behind this sudden fall and what measures you can take to regain impressions on your content. Let’s dive in to explore everything in detail.

Primary Reason Behind This Impression Drop: The &num=100 Change

In mid-September 2025, a quiet but seismic shift unfolded. If your impressions suddenly dropped, there’s a high chance you were hit by what many in the SEO world are calling the num=100 change.

What changed?

  • Google appears to have quietly disabled support for the URL parameter &num=100, which was widely used (especially by SEO tools) to fetch up to 100 search results in one request instead of the default 10.

What difference does it make?

  • Many SEO tools and scrapers were using num=100 to fetch up to 100 results per query, thereby tracking many lower-ranking URLs. Those bots may have bought impressions in GSC for many sites.
  • However, with &num=100 disabled, those bot-driven “far past page 1” impressions get cut off. This, in turn, reduced the number of “impressions” those automated tools generated on any site.

For some, it also caused an increase in average position

  • Many site owners report steep drops, especially on desktop impressions, along with an apparent improvement in average position. That is, with fewer extraneous impressions counted, the average ranking looks better.
  • As a result of this change, top industry experts suggest that when num=100 was used, some of the impression numbers in GSC were inflated by bot or scraping requests. With all those impressions cleaned out, the currently ranking data is leaner and more realistic.

In short

  • Many sites are seeing impression drops not because their SEO performance collapsed, but because Google redefined what counts as an actual impression, removing the noise.

Other Key Reasons Why GSC Impressions May Decline

Even if &num=100 is the big recent shake, here are some possibilities of why GSC impressions may fall:

1. Google’s Algorithmic Updates

Google regularly updates its ranking algorithms and how it evaluates content, relevance, freshness, E-A-T, etc. A core update or relevance rebalancing can shift which pages get surfaced more often.

If your content is seen as less relevant, outdated, or inferior to competitors, you may lose impressions.

2. Indexing / Crawling Issues

Pages dropping out of the index due to robots.txt, noindex tags, sitemap changes, or errors will lose impressions.

3. Search Intent Shifts & Query Trends

User behaviour evolves. A topic may wane in popularity, or search phrasing may change. If many of your high-impression queries fall out of favour or the query landscape shifts, you lose impressions even if you rank well.

4. Technical SEO problems

Server downtime, broken canonical tags, redirect chains, or changes in URL structure can block Google from accessing pages.

5. Increased Competition/ Query Cannibalisation

New competitors or content changes could push your pages down. Or you may be unintentionally competing with your own pages.

6. Manual Penalties or Spam Filters

Less common but critical: if your site triggers a penalty or gets flagged for policy violations, pages may be suppressed. You’ll often see notifications in GSC.

7. Content Quality / Relevancy Decay

Maybe competitors have produced fresher, more authoritative versions on the same topic. If Google deems your content to have a lower value, it may reduce how often it surfaces.

GSC’s impression drop may have multiple factors working behind the scenes. If you tangled here, hire an SEO expert and let them help you get your impressions back on track.

How to Diagnose What’s Causing GSC Impression Drop?`

Now comes the detective work. Use the data in GSC and external tools to triangulate the cause. Here’s a step-by-step approach you can use to find the root cause:

Step 1: Look for the infection point

  • In GSC, set the date range and compare to a previous similar period (e.g., week vs week, month vs month, or year-over-year).
  • Look for when the drop began (the infection point)
  • Was that timing near the &num=100 change (mid-September 2025)? That might immediately point you to a measurement shift rather than an SEO loss.

Step 2: Check whether the drop is site-wide or in segments

  • Use filters by query, page, country, device, and search appearance to isolate where the impression decline lives.
  • Sort your pages by the highest impressions previously. Which ones dropped the most?
  • For queries, see if formerly ranking queries have disappeared entirely from the impressions list.

Step 3: Cross-check on Google Analytics (GA4)

  • If your organic traffic is flat or only slightly changed while GSC impressions collapsed, that strongly suggests a measurement artifact rather than a real drop.
  • If both GSC impressions and GA4 sessions dropped in tandem, that’s more serious—it may mean real loss of visibility.

Step 4: Inspect Indexing Section

  • Navigate to the indexing section in your GSC, and check whether there are any new 404, server errors, excluded pages, or redirect issues.
  • Try to solve those issues at the earliest to get impressions on track.

Step 5: Check for External Shifts

  • Keep a check on Google’s official Search Central Blog or reliable third-party sources to see if any core update is rolled out
  • Use Google Trends to check if the overall query volume for your domain’s keywords dropped (i.e., fewer people searched)

Step 6: Look for penalty signals

  • Check if Google Search Console’s Security & Manual Actions section shows warnings or security issues.
  • Use a backlink audit to see if there was a sudden influx of toxic links or unnatural linking patterns.

Step 7: Crawl & technical audit

  • Use audit tools like Screaming Frog, Sitebulb, etc., to check for new 404s, broken links, redirect loops, robots.txt changes, or sitemap issues.

Once you gather evidence, you can narrow it down to whether this is a measurement change (num=100) or a real visibility issue. Then you can apply the appropriate fixes.

SEO Expert-Approved Impression Recovery Solutions

Once you find the root cause, here are tactics you can use to recover and stabilize:

If it’s Due to Disabling num=100 param

  • Don’t panic because the “loss” is in reported impressions, not necessarily in real visibility.
  • If you report to stakeholders, explain to them that the metric shift is primarily driven by Google’s filter change, not site decline.
  • Your new normal for impressions will be lower, so reset your benchmarks and targets accordingly.
  • Monitor SERP position stability for your priority queries. If they hold steady, you likely didn’t lose real visibility.
  • Keep an eye on future updates; Google may adjust reporting further.

If Anything Else Caused the Collapse: Indexing or Technical Issues

  • Refresh or rewrite underperforming pages. Expand or improve content depth & re-optimize them according to current search intent.
  • Strengthen internal linking and site architecture to help Google rediscover and re-rank those pages.
  • Be patient. Recovery from algorithmic shifts can take weeks to months.
  • Submit a new XML sitemap and request a recrawl via URL Inspection.
  • If old queries decayed, find new long-tail or related queries to get fresh impressions.
  • If SERP featured post snippets are replacing your content, try to optimize for those features by adding structured data, FAQs, and to-the-point information.
  • Track competitor content, see what’s changed, what new features they added, or what keywords they’re now targeting.
  • If nothing works, accept that some drops are natural and give time to change your site’s content accordingly.
  • Create seasonal content ahead of time for rebounds.
  • If a penalty issue arises, remove spammy or duplicate content. Add fresh and authoritative content to fortify your site’s reputation again.

Over time, you should see impressions and rankings climb back for high-value pages if your fixes are well aligned.

Impact on SEO/Marketing Future

This shift strongly suggests that SEO experts think out of the box to keep up with modern ways of ranking your content.

  • Impressions are losing importance as a KPI. Instead, rely more on clicks, CTR, conversions, and organic sessions.
  • Focus on ranking in the top 10-20 results because this shift made it clear that lower-ranking pages (>20) will disappear sooner.
  • Keep your content intent clear and to the point to keep it authoritative.
  • Prepare stakeholders that the metric landscape is changing and present more meaningful metrics (CTR, conversions) while showing them your work.
  • Diversify channels, own your content brand, focus on quality, and maintain measurement flexibility.

Conclusion & Key Takeaways

If your Google Search Console impressions have recently dropped, it doesn’t necessarily mean your SEO efforts are failing. For instance, the recent num=100 change has altered how impressions are counted, causing many websites to appear as though they’ve lost visibility even when rankings and traffic remain stable.

Instead of reacting in panic, you need to respond with analysis. The key solution here is to diagnose before reacting and to interpret metrics through the right lens. For that, you can monitor your data, compare timeframes, review indexing and technical performance, and evaluate whether this drop truly reflects a loss of visibility or just a reporting adjustment.

At TRooInbound, we help businesses approach moments like this with clarity and strategy. Our approach focuses on connecting data signals across GSC, Analytics, and keyword trends to identify what’s really changing and what actions will make the biggest impact. If you ever need expert help decoding those shifts, TRooInbound is always ready to guide you with data-driven insight and proven SEO expertise.

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