The Billing Model That Makes Your Agency Want You to Overspend
Percentage-of-spend is the most common billing structure in performance marketing. It's also the one with the most broken incentives.
Colt & Co.
Revenue Architecture
Definition
Percentage-of-Spend Billing Percentage-of-spend (also called % of spend) is a performance marketing agency billing model where the agency charges a percentage of the client's total advertising budget as their monthly fee — typically 10–20%. The agency's revenue is directly tied to how much the client spends on ads.
This is the most common billing model in the performance marketing industry. It's also the one with the most structurally broken incentives.
The Incentive Problem
Under a percentage-of-spend model, the agency earns more when you spend more. That's the entire incentive structure. It means that every budget conversation has a built-in conflict of interest: the agency recommending a higher budget is the same agency that earns a percentage of that budget.
This doesn't mean every percentage-of-spend agency will recommend unnecessary budget increases. But the model's incentives don't reward efficiency. There is no financial benefit to the agency for reducing your spend and improving your ROAS. There is a direct financial benefit to recommending budget scaling.
| Scenario | Percentage-of-Spend Agency | Fixed Retainer Agency |
|---|---|---|
| Client's ROAS drops | Recommends higher spend to 'test' recovery | Diagnoses root cause — their fee doesn't change either way |
| Campaign efficiency improves | Recommends scaling spend to 'capture opportunity' | Documents the win; focuses on next efficiency gain |
| Budget reduction needed | Resistance — revenue drops proportionally | Neutral — revenue unchanged |
| Agency incentive | Higher spend = higher fee | Better performance = client growth = contract renewal |
| Typical fee | 10–20% of spend | Fixed monthly, spend-agnostic |
The Fixed Retainer Model
A fixed retainer doesn't scale with spend. The agency earns the same fee whether you spend ₹5L or ₹50L/month. This means the agency's only lever for growing their revenue is improving your results enough that you want to expand the engagement — not recommending budget increases.
Colt & Co. billing
Colt & Co. operates exclusively on a fixed monthly retainer. No percentage of spend. Our fee is the same whether we reduce your budget by 20% and improve ROAS by 60%, or maintain your current spend. We grow with you by performing — not by invoicing.
How to Evaluate Agency Billing Models
- Ask: 'What happens to your fee if I reduce my ad spend by 30%?' — A percentage-of-spend agency loses revenue. A fixed retainer agency doesn't. The answer tells you where their incentives sit.
- Ask: 'Have you ever recommended a client reduce their spend?' — If the answer is never, that's the percentage-of-spend model at work.
- Ask: 'How do you measure success?' — If the answer is primarily ROAS (a platform-reported number they partially control by recommending spend levels), that's a flag.
- Ask: 'What attribution model do you use?' — If they use platform last-click, they're reporting the number the platform wants you to see, not the number that reflects actual revenue.
Frequently Asked Questions
Is percentage-of-spend always a bad model?
Not always — at very early stages when spend is low and the agency's work is heavily campaign-execution focused, percentage-of-spend can align incentives reasonably well. The model breaks down as spend scales and the gap between 'more spend' and 'better results' widens.
What should a fixed retainer for performance marketing cost?
Fixed retainer pricing varies by scope and spend level. At Colt & Co., retainer tiers are calibrated to managed spend volume — not as a percentage, but as a fixed fee that accounts for the complexity of the revenue system being managed. The Revenue Diagnostic establishes scope before any engagement begins.
Why do most agencies use percentage-of-spend?
It's easier to sell and scales naturally with the client relationship — as the client grows, the agency's revenue grows automatically without renegotiating fees. The downside is that it also grows automatically when clients overspend, not just when they grow efficiently.
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