Negative keywords are the most consistently high-return activity in Google Ads management. When I audit accounts, the search terms report is usually the first place I look, and the waste I find there, in clicks going to searches that have no chance of converting, is almost always significant. In accounts with no negative keyword strategy, 20 to 40% of spend on irrelevant traffic is not unusual. For a trade business in Llandudno or Wrexham spending £500 a month on ads, that's potentially £100 to £200 a month reaching people who were never going to become customers.
I audited a joinery business in Anglesey last year whose account had been running for ten months without a single negative keyword added. The search terms report showed spend going to "joinery apprenticeships near me," "joinery courses online," "what is joinery," and a cluster of DIY tutorial searches. Around 30% of their monthly spend, close to £180, was going to people who had no intention of hiring anyone. Adding a shared negative list took about an hour. It effectively gave them a 30% budget increase with no additional spend.
The common assumption is that broad match is the culprit for this kind of waste. It is, but it's not the only one. Phrase and exact match keywords are now matching more broadly than they used to, meaning negative keyword work is necessary regardless of which match types you're using.
The fix is straightforward. The ongoing habit is what most advertisers don't maintain.
What are negative keywords and how do they work?
Your keywords tell Google what searches you want to appear for. Negative keywords tell Google what searches you explicitly don't want to appear for.
When you add a term as a negative keyword, Google excludes your ad from showing when that term is present in the search query. If you're a plumber advertising "boiler repair," and someone searches "boiler repair training course," the word "training" as a negative keyword would prevent your ad from showing for that search.
The reason this matters so much is the gap between what you bid on and what people actually type. Your keywords are what you choose. Search terms are what people type. These two things diverge, sometimes significantly, depending on your match types. Broad match in particular is highly permissive, as it can match your keywords to searches that are only thematically related, and match types have broadened significantly over the years, making negative keywords more important than ever. If you're new to how match types work, the top budget-killing mistakes beginners make covers match types and two other default settings that commonly destroy early campaign performance.
The search terms report (Keywords > Search terms in Google Ads) shows every query that triggered your ads. Comparing it to your keyword list reveals where budget is leaking.
Match types for negative keywords
Negative keywords use the same match type logic as regular keywords: broad, phrase, and exact.
Negative broad match excludes searches containing any of the words in any order. Adding "free" as a negative broad match keyword prevents your ads showing for "free plumber," "free boiler service," and "plumber free quote." Use this for excluding entire concept areas.
Negative phrase match excludes searches that contain the specific phrase in that order. Adding "how to" as a negative phrase match excludes "how to fix a boiler" and "how to service a radiator" without affecting queries that don't contain that sequence.
Negative exact match excludes only that specific query. Adding [boiler repair manual] as an exact negative only prevents your ad showing when someone searches exactly that phrase. It doesn't affect other queries containing those words.
For most accounts, a mix of negative broad match (for concept-level exclusions like "jobs," "training," "DIY," "free") and negative exact match (for specific irrelevant queries identified in the search terms report) is the right approach.
Building your negative keyword list
There are two sources for negative keywords: proactive research before launch, and reactive additions from the search terms report after launch.
Before launch, think through all the searches that might vaguely trigger your keywords but would never convert. The most common categories to exclude: searches containing "free," "cheap," or "DIY" where the searcher is looking for tutorials or self-service options, not someone to hire; job and career searches like "[service] jobs near me" or "[industry] apprenticeships"; training and course searches targeting people who want to learn the trade rather than hire it; geographic modifiers for areas you don't serve; and competitor brand names if you don't want to show for those queries and pay the typically higher CPCs.
After launch, open the search terms report at least weekly. Filter by date (last 7 days or last 30 days), sort by cost, and look for queries spending without converting. Add these to your negative keyword list at the campaign level, or at the ad group level if the exclusion is specific to a particular ad group.
Negative keywords at campaign vs. account level
Negatives can be added at campaign level (applying only within that campaign) or at account level through a shared negative keyword list (applying across multiple campaigns simultaneously).
For exclusions that apply everywhere, such as "free," "training," and "jobs," a shared negative list is more efficient. You add the term once and it applies across every campaign that uses the list. For exclusions specific to a particular campaign's targeting, add them at the campaign level.
To create a shared negative keyword list: Tools > Shared library > Negative keyword lists. Create a list, populate it with your universal exclusions, then attach it to the relevant campaigns.
The common mistakes
Adding negatives too aggressively is the main one. A negative phrase match for "how to" might also exclude "how to contact us" or "how to book," which are searchers with intent. Check that your negatives don't inadvertently exclude converting terms. Review the search terms report after adding new negatives to catch any unintended exclusions.
Not reviewing often enough is also common. New search terms appear continuously as people's search behaviour evolves and as Google's matching algorithms change. Weekly is the minimum cadence for accounts with meaningful spend. Fortnightly is acceptable for lower-spend accounts. Monthly is not enough.
The third mistake is relying on negative keywords instead of fixing match types. Negatives are essential, but they're a filtering mechanism, not a substitute for using appropriate match types. If you're running broad match without phrase or exact match alternatives for your core terms, negatives will reduce waste but not eliminate it. Tighter match types reduce the volume of irrelevant triggers in the first place. For accounts on limited budgets where every click counts, 3 Targeting Tweaks to Optimise Limited Google Ads Budgets covers how match types, negative keywords, and ad scheduling work together to stretch a restricted budget further.
Google Ads management in North Wales: if you'd like a free audit showing exactly what your search terms report reveals about wasted spend, get in touch.
