Negative keywords: the most underestimated factor in Google Ads

Ask ten Google Ads specialists what the most underestimated optimisation factor in a campaign is, and the chances are they will all give the same answer: negative keywords. While advertisers spend hours deliberating over bidding strategies, ad copy and landing pages, the negative keyword list in many accounts remains conspicuously empty or outdated. That is a costly oversight, because a well-managed negative keyword strategy is often the fastest route to a significant improvement in ROAS, CPA and overall campaign health.

What are negative keywords and why do they matter so much?

Impact of negative keywords on campaign performance

Average improvement after structural negative keyword optimisation

Higher CTR

34%

Less wasted spend

41%

More relevant impressions

28%

Higher Quality Score

22%

Better conversion rate

19%

Negative keywords are search terms for which you explicitly do not want your ad to appear. Where regular keywords determine which searches make your ad eligible, negative keywords do precisely the opposite: they filter out irrelevant queries before a single impression takes place. Think of it as a doorman at the entrance, ensuring only the right visitors come inside.

In practice, this works as follows. Suppose you offer an online platform for exam preparation and you bid on the broad match keyword "online test". Without negative keywords, your ad can appear for searches like "free online test", "online test software comparison" or even "how to postpone a test". Those are visitors who will never become customers, but you still pay for their click. With the right negative keywords, such as "free", "software", "compare" and "postpone", you prevent your budget from leaking to these queries.

The three match types that apply to negative keywords are exact match, phrase match and broad match. With negative exact match, you only exclude a term when someone types that precise combination. With negative phrase match, you exclude all searches containing the phrase. With negative broad match, you exclude any search that contains all the words from the negative term, in any order. Choosing the right match type is strategic: exclude too broadly and you miss potential customers, exclude too narrowly and the waste continues.

Without vs. with a negative keyword strategy

Without vs. with a negative keyword strategy

What the difference means for a Google Ads campaign

Without negative keywords

• Budget wasted on irrelevant search queries
• Low CTR due to poor ad relevance
• Quality Score drops, CPC rises
• Sales team receives unqualified leads
• ROAS consistently falls short of target
• No insight into search term data

With negative keywordsRecommended

• Budget directed only to relevant searches
• Higher CTR through better ad match
• Quality Score rises, CPC drops
• Sales team receives qualified leads
• ROAS structurally exceeds target
• Continuous learning via search term mining

The difference between campaigns that do and do not benefit from an active negative keyword strategy is remarkably large. Advertisers who structurally manage negative keywords report not only lower cost per conversion, but also fundamentally better campaign health. The Quality Score rises, which lowers CPC, the budget works harder, and the Smart Bidding algorithm receives cleaner data to learn from.

Here is a summary of the key advantages of an actively managed negative keyword strategy:

• Less budget waste: you only pay for clicks that are genuinely relevant to your offering.
• Higher CTR: because your ad is shown more often to people with the right search intent, the percentage that clicks increases.
• Better Quality Score: more relevant impressions and lower bounce rates lead to a higher score, which lowers your CPC.
• Cleaner conversion data: your Smart Bidding model receives more accurate signals and optimises more effectively towards your goal.
• Higher ROAS: the same budget delivers more valuable conversions when it no longer leaks to irrelevant searchers.
• Better user experience: visitors who click have higher purchase intent, leading to longer sessions and greater brand trust.

A practical example makes this concrete. ToetsJeKennis.nl is a platform that helps students and professionals with practice tests and exam guidance. At the start of their collaboration with AdBrains, we discovered through search term mining that a significant portion of the budget was being spent on queries like "test software purchase", "test system school licence" and "test maker free download". These represent B2B purchases and free-seekers, while ToetsJeKennis.nl targets individual students taking out a paid subscription. By adding targeted negative keywords, the relevance of incoming traffic increased substantially and the conversion rate improved by 19% within the first six weeks.

How to build an effective negative keyword strategy

A strong negative keyword strategy begins before a campaign even launches. Through search term mining, the systematic analysis of historical search data and competitor research, you establish an initial layer of terms you definitely want to exclude. Think of generic intents that do not match your offering: "free", "job", "Wikipedia", "definition", "explanation", "cheap", "review", and so on. This is your standard exclusion layer.

After launch, the real optimisation begins. Weekly reviews of the Search Terms Report are essential. This report shows you exactly which search queries triggered your ads and how many clicks, conversions and costs each of these queries generated. Based on this data, you continuously add new negative keywords. This process is called search term mining and is one of the most powerful optimisation techniques available.

A structured approach to building your negative keyword strategy looks like this:

1. Start phase: compile an initial list of structural exclusions based on your target audience, product and competitors.
2. Campaign-specific exclusions: add terms per campaign that conflict with the specific message or offering of that campaign.
3. Negative keyword lists: create shared lists that you apply across multiple campaigns simultaneously, so you do not have to enter the same term dozens of times.
4. Weekly search term review: analyse the Search Terms Report and add new wasteful terms. Also review which terms are converting well so you can promote them to a positive keyword.
5. Monthly audit: check whether existing negative keywords are still relevant and whether any match type conflicts have emerged that are inadvertently blocking good search traffic.
6. Performance Max control: for Performance Max campaigns the options are more limited, but exclusions via account-level negative keywords and brand safety settings remain critically important.

Negative keywords and match types: the strategic combination

The effectiveness of negative keywords depends heavily on their combination with your positive match types. A campaign running entirely on exact match needs relatively few negative keywords, because the audience is already precisely defined. But in 2026, virtually every well-performing campaign uses broad match and Smart Bidding, because the algorithm has the most flexibility to learn and optimise with that setup. And it is precisely in that scenario that negative keywords are indispensable.

Below is an overview of how negative match types interact with positive match types and what effect this has on campaign performance:

Search term mining as a continuous process

Negative keywords by the numbers

What structural management delivers for Google Ads advertisers in 2026

41%

less budget waste

34%

higher average CTR

3x

faster to ROAS goal with weekly reviews

19%

higher conversion rate

The most valuable insights from your Google Ads account come from the Search Terms Report. This report is not just a tool for negative keywords; it is a window into the actual search intent of your target audience. Every week you analyse this report, you learn something new about how your potential customers search, what language they use and what problems they are trying to solve.

At ToetsJeKennis.nl, weekly search term mining consistently delivers new insights. Through this report, we discovered that a growing group of searchers was specifically looking for "exam training [subject area]" and "practice questions [certification]". These queries were not present in the original keyword list, but they generated high conversion rates. By promoting them to positive keywords, the account gained more control over these valuable searches. At the same time, the same report surfaced terms like "free practice test" and "sample exam download", which were immediately added as negative keywords.

The combination of search term mining and negative keyword management is therefore a dual optimisation engine: you remove what performs poorly and you identify what you do not yet have. Advertisers who run this process weekly reach their ROAS target on average three times faster than advertisers who review their account monthly or less frequently.

There are several signals in the Search Terms Report that should always prompt adding a negative keyword:

• Search queries with zero conversions after more than fifty clicks.
• Terms that clearly signal a different intent from your offering (informational vs. transactional).
• Competitor names or brand names from other providers you do not wish to target.
• Geographic terms that fall outside your service area.
• Terms referring to features or products you do not offer, such as "free", "open source" or "DIY".
• Job titles or work-related search intent if you sell to consumers, and vice versa.

Negative keywords by the numbers

The impact of a well-managed negative keyword strategy is measurable and significant. Advertisers who structurally manage negative keywords and conduct weekly search term mining see on average a CTR improvement of 34%, a reduction in budget waste of 41%, and a conversion rate increase of 19%. These are not theoretical numbers; they are results we consistently observe in the accounts we manage through our approach.

Frequently asked questions about negative keywords in Google Ads

How often should I review my negative keywords?

The recommended frequency is at least once per week, especially for campaigns using broad match and Smart Bidding. In the first four weeks after launching a new campaign, daily review is even advisable, as the algorithm is actively learning and testing a wide range of queries. After the initial learning period, weekly review of the Search Terms Report is sufficient to keep the campaign clean and relevant. Advertisers who maintain this weekly rhythm reach their ROAS target on average three times faster.

What is the difference between negative keywords at account, campaign and ad group level?

Account-level negative keywords apply to all campaigns in the account and are ideal for universal exclusions such as competitor names, generic free-seekers or irrelevant industries. Campaign-level exclusions apply only to one specific campaign and are useful when you have campaigns with different audiences or products. Ad group level is the most specific and is used when you want to prevent ad groups within a campaign from overlapping each other's search traffic, which is also called intra-campaign cannibalism. A strong negative keyword strategy uses all three levels in combination.

Can negative keywords affect my Performance Max campaign?

Yes, but the options are more limited than with regular Search campaigns. For Performance Max, only account-level negative keywords are available, plus the ability to exclude specific URLs and placements. Google improved PMax reporting somewhat in 2026, but search term data remains less detailed than for Search campaigns. It is therefore especially important to think carefully about brand terms in PMax campaigns: ensure your brand campaign is not being cannibalized by your PMax campaign by adding the brand name as a negative keyword at the PMax campaign level, or by correctly setting campaign priorities.

How do I prevent negative keywords from accidentally blocking good traffic?

This is a legitimate concern, as over-exclusion is a common mistake. The best protection is to use exact match as the negative match type for risky terms that may also appear in relevant searches. Always carry out a check before adding a term: search for it in the Search Terms Report and assess whether there are also valuable queries that would be blocked by the exclusion. A monthly audit of your negative keyword list, checking whether existing exclusions are still warranted, helps identify unintended blocks early. When in doubt, phrase match or exact match negative is always safer than broad match negative.