Google Ads Doesn't Have a Budget Problem. It Has a Margin Problem.
"What should our Google Ads budget be?" is the wrong question. The right question: "At what point does the next pound spent return less than our minimum acceptable margin?"
The Default Approach
Most brands set Google Ads budgets based on what finance approves, what was spent last year plus 10%, or what the agency suggests. None of these methods have any relationship to the actual economics of each product being advertised.
The Budget Fallacy
A budget is a constraint. A margin target is a strategy. The difference matters because constraints are arbitrary while strategies are derived from commercial reality.
When you set a £50,000 monthly budget, you are saying: "Spend this regardless of whether the last £10,000 makes money." When you set a margin floor, you are saying: "Spend until it stops being profitable, then stop."
One approach scales naturally. The other creates artificial ceilings and floors that have nothing to do with opportunity.
Margin, Not Budget
The economics of Google Ads follow a diminishing returns curve. The first £10,000 captures high-intent, high-converting traffic. The next £10,000 pushes into broader queries with lower conversion rates. The next £10,000 starts competing for traffic that barely breaks even.
The right budget is wherever that curve crosses your margin floor. Some months that is £30,000. Some months that is £80,000. A fixed monthly budget ignores this entirely.
"Budget is an input. Margin is an outcome. Optimise for outcomes."
SKU-Level Truth
A £50 product with 70% gross margin can sustain £15 in advertising cost per sale and still contribute £20 to the business. A £50 product with 30% gross margin cannot sustain any meaningful ad spend without losing money.
Yet most Google Ads accounts treat both identically. Same campaigns, same bidding strategy, same targets. The high-margin product subsidises the low-margin product, and the blended ROAS masks the problem.
High-Margin SKU
70% gross margin. Can sustain aggressive bidding, broad matching, and prospecting campaigns. Every additional sale adds real contribution.
Low-Margin SKU
30% gross margin. Needs restrictive bidding or exclusion from paid entirely. Each sale at competitive CPC destroys contribution margin.
The fix is not complicated. Feed your margin data into the bidding strategy. Use conversion value rules to weight high-margin products. Exclude or cap bids on products where the economics do not work. This is not optimisation. It is basic commercial sense.
Dynamic Ceilings
In a margin-based framework, budgets flex with opportunity. During peak demand periods, marginal returns improve because conversion rates rise. The budget should expand. During off-peak, marginal returns deteriorate. The budget should contract.
This is the opposite of how most brands operate. They set annual budgets in Q4, divide by 12, and adjust reluctantly. Opportunity is left on the table in strong months and money is wasted in weak ones.
A dynamic approach requires trust between marketing and finance. Finance needs confidence that more spend means more profit, not just more activity. That confidence comes from SKU-level margin reporting, not ROAS dashboards.
The Reframe
Stop asking "what should our budget be?" and start asking "what is our marginal return curve?" The first question invites politics. The second invites maths.
Brands that make this shift typically find they are simultaneously overspending on low-margin products and underspending on high-margin ones. The total budget might not change. The allocation changes completely. And profit follows.
Next Steps
The Bottom Line
Google Ads does not have a budget problem. It has a margin problem disguised as a budget problem. Fix the margin visibility and the budget conversation solves itself.
Talk Margin, Not Budget