Negative keywords: the most underestimated factor in Google Ads

Negative keywords are search terms you explicitly exclude in Google Ads, preventing your ads from appearing on irrelevant queries. They are the most direct lever to stop wasted spend, improve incoming traffic quality, and give Smart Bidding the right signals to optimise. Yet most advertisers apply negative keywords too late, too sparingly, or without structure.

Key takeaways

• Negative keywords exclude irrelevant queries and protect your campaign budget directly.
• They operate at campaign and ad group level, and can be bundled into shared lists.
• Structural search term mining is essential to keep negative keyword lists up to date.
• Smart Bidding learns better when it receives conversion signals from relevant clicks only.
• AdBrains automates daily search term mining with AI, including multi-agent verification for every addition.

What are negative keywords and how do they work?

A negative keyword is a term you explicitly exclude from a campaign or ad group. When someone searches for a query containing your negative keyword, your ad is not shown. This sounds straightforward, but the application requires precision. Just like regular keywords, negative keywords exist in exact match, phrase match, and broad match exclusion types, and that choice directly determines which queries you block.

Take E-4motion.com, which sells exclusively new electric folding bikes. Adding "second hand" or "used" as broad match negative keywords immediately prevents the ads from showing on queries like "second hand e-bike" or "used electric bike Amsterdam". These clicks would never convert into a new bike sale, and excluding them protects both budget and Smart Bidding's learning data.

Negative keywords operate on two levels:

• Campaign level: the exclusion applies to all ad groups within that campaign.
• Ad group level: the exclusion applies only to that specific ad group, allowing more granular control within a single campaign.

You can also build negative keyword lists in the Google Ads shared library and attach them to multiple campaigns at once. This is far more efficient than adding the same terms manually to each campaign and ensures consistency across your account.

Why negative keywords are so consistently underestimated

Common reasons for irrelevant clicks in Google Ads

Percentage of advertisers reporting this as a problem (Think with Google, 2026)

Broad match types without negative keywords

61%

No structural search term mining

54%

Missing negative keyword lists

47%

No distinction between campaign and ad group level

38%

Most attention during campaign setup goes toward the positive side: which keywords to target, which ad copy to write, what budget to set. Negative keywords are treated as an afterthought. That is an expensive mistake.

Without an active negative keyword strategy, you pay for clicks from people who never intended to buy or request a quote. With broad match or phrase match, Google expands your keywords to related variants, significantly increasing the chance of irrelevant impressions. According to Think with Google (2026), more than 60% of advertisers use broad match types without structured negative keyword lists.

The impact on Smart Bidding is equally serious. Google's algorithm learns from conversion data. If a significant share of your clicks comes from irrelevant queries that never convert, that corrupts the learning process. Your Target CPA or Target ROAS strategy receives a distorted picture of which signals lead to conversions, which structurally undermines bidding performance.

Negative keywords strategy for Google Ads in B2B

For B2B advertisers, negative keywords are especially critical. The search intent of a B2B buyer differs fundamentally from a consumer, and the queries overlap enough to cause real problems. A B2B company offering commercial air conditioning installation does not want enquiries from consumers searching for a small portable unit.

A solid negative keywords strategy for Google Ads in B2B always includes exclusions for:

• Consumer-oriented terms ("cheap", "DIY installation", "for home use")
• Informational queries without purchase intent ("how does a heat pump work", "heat pump explained")
• Free alternatives ("free quote template", "calculate yourself")
• Geographic exclusions if you only operate in specific regions
• Competitor brand names where relevant

Clima-Active.nl, which generates leads for air conditioning and heat pump installation, benefits directly from this approach. Someone searching for "buy air conditioner MediaMarkt" or "rent portable airco" has no installation need. Those clicks are expensive noise.

How AdBrains automates negative keywords with AI

AdBrains has built an automated search term mining system that goes through every search term generating traffic across active campaigns, every single day. Not a periodic review, but a continuous process running at the level of each individual ad group.

The system flags search terms that don't fit campaign intent, using several criteria: no clicks, no conversions, a semantic match that's clearly off, or exclusion patterns defined in an earlier round. A flagged term doesn't become a negative keyword straight away. It goes to a multi-agent verification layer first, where four independent AI agents each assess the proposed exclusion. The purpose is straightforward: make sure no relevant queries get accidentally blocked. The addition only goes through once there's consensus.

Manual management vs. AI automation for negative keywords

How the approach differs in practice

Manual management

• Monthly or weekly search term review
• Manual addition of irrelevant search terms
• Risk of missing irrelevant queries at scale
• No systematic list structure
• Little distinction between campaign and ad group level

AdBrains AI automationAdBrains AI

• Daily analysis of all search terms per campaign
• Automatic detection and addition as negative keyword
• Multi-agent verification prevents errors on addition
• Structured negative keyword lists per campaign type
• Campaign vs. ad group level distinction maintained

That's the real difference from manual management or basic rule-based automation. Accounts reviewed manually on a weekly cadence routinely miss search terms that have been draining budget for weeks before anyone catches them. With daily AI-driven mining, that window shrinks to 24 hours at most.

On top of the daily mining, AdBrains builds structured negative keyword lists per client and per campaign type. For ToetsJeKennis.nl, a platform selling online exams and courses at an average order value of around 50 euros, that means maintaining exclusion lists for terms like "free", "answers", "cheat sheet" and similar queries that clearly aren't coming from someone ready to pay for a certified exam. As new irrelevant patterns show up, those lists get expanded automatically.

The Keyword Incubator ties into this as well. New keywords tested in a separate incubator campaign generate search term data that feeds straight back into the negative keyword system. Over time, and based on real campaign data rather than guesswork, the line between relevant and irrelevant becomes considerably sharper.

Match types for negative keywords: exact, phrase, and broad

Choosing the right match type for negative keywords has more impact than most advertisers realise. Here is an overview of the three types and when to use each:

A common mistake is using exact match negative as the default, which blocks only that precise query while variants continue to reach your ads. Conversely, an overly broad exclusion on broad match level can block relevant queries. The right choice requires understanding search intent and campaign structure.

Search term mining: the foundation of any negative keyword strategy

Effect of negative keywords on search traffic

Example: Search campaign with active negative keyword strategy (per month)

All impressions

Total shown based on broad/phrase match

Filtered by negative keywords

Irrelevant queries excluded

Clicks on relevant ads

Higher CTR through better targeting

Conversions

More conversions per euro spent

Less wasted budget, higher ROAS

Search term mining means systematically analysing the search terms report in Google Ads to identify which queries actually drive traffic to your ads. The report shows exactly what people typed, as opposed to the keywords you bid on. With broad match and phrase match especially, that gap can be surprisingly wide.

A workable search term mining routine looks like this:

1. Open the search terms report at ad group or campaign level.
2. Filter for search terms with no conversions and multiple clicks.
3. Assess whether the search intent matches your offering.
4. Add irrelevant terms as negative keywords at the right level (campaign or ad group).
5. Consider adding converting new terms as positive keywords to an existing or new ad group.
6. Repeat this process at minimum weekly, daily for high-volume campaigns.

Step five tends to get overlooked. The report tells you not just what to cut, but where you may be leaving money on the table. If a search term converts but sits outside your keyword list, you have no real control over how aggressively you bid on it. That is a problem worth fixing.

Negative keywords in Performance Max campaigns

Performance Max (PMax) offers less direct control over search terms than standard Search campaigns. Google largely decides where and when ads appear. Negative keywords can be added in PMax, but the options are more limited: you can only apply them at campaign level or via shared lists, not at the Asset Group level.

Even so, negative keywords remain important in PMax. Without exclusions, a PMax campaign risks optimising on signals from irrelevant impressions. For HACCP-cursus.com, which offers food safety courses to professional users, excluding terms like "free", "recipe", or "food storage tips" keeps the campaign focused on participants with a genuine training need. Google Ads Help (2026) confirms that negative keywords in PMax operate at exact match and phrase match level and restrict Asset Group targeting accordingly.

Frequently Asked Questions

What are negative keywords in Google Ads and why do they matter?

Negative keywords are search terms you exclude from your campaign so your ads do not appear on irrelevant queries. They matter because they prevent wasted spend, improve incoming traffic quality, and give Smart Bidding better conversion signals. Without negative keywords, you pay for clicks that will never convert, which pushes up CPA and reduces ROAS.

How does a negative keywords strategy for Google Ads in B2B differ from B2C?

In B2B you exclude different terms than in B2C. B2B advertisers want to block consumer queries, informational questions without purchase intent, and terms like "DIY" or "for home use". In B2C, exclusions more often filter out wrong product variants, incorrect audiences, or purely informational searchers. The fundamental approach is the same, but the word lists are market-specific.

Negative keywords can help advertisers refine the targeting of their ads by doing what exactly?

Negative keywords help advertisers refine targeting by excluding queries that lack the right purchase intent. In practice this means fewer impressions to people outside the target audience, a higher CTR on remaining impressions, better Quality Scores on relevant search terms, and ultimately a lower CPA or higher ROAS. According to Google Ads Help (2026), negative keywords improve both impression relevance and overall campaign efficiency.

How often should I update my negative keyword lists?

Ideally daily for large campaigns with high search volume, and at minimum weekly for smaller campaigns. User search behaviour changes continuously, and Google's match type interpretations are regularly adjusted. A negative keyword list you compiled three months ago is likely incomplete today. At AdBrains this is handled daily through automated search term mining, so no budget is lost to irrelevant queries for more than 24 hours at a time.