Business growth agency: what it does, how the fees are built and how to judge the first ninety days

A business growth agency is a firm that takes responsibility for moving a commercial number, such as new customers, revenue or qualified leads, by running a steady series of experiments across marketing, sales and the product experience. Hire one when you have a product people buy and a number you want to move. Agree the number, the budget, the experiment cadence and the reporting before the first month starts.

This guide explains what the work includes, the fee models, when to hire, how to brief the agency and how to judge it after ninety days.

What a growth agency does

A growth agency differs from a traditional marketing agency in its method. It starts from data on how customers find, try and keep your product, picks the part of that journey with the biggest gap, and tests changes there. The work typically covers:

• Measurement. Setting up analytics, tracking events and a dashboard that shows the funnel from first visit to repeat purchase.
• Acquisition. Search, paid media, social, partnerships and outbound, chosen by cost per customer.
• Conversion. Landing pages, sign up flows, pricing pages and checkout, improved through tests.
• Activation and retention. Onboarding emails, in-product prompts and win back campaigns.
• Experiment management. A backlog of ideas, a priority order, a test plan and a record of results.

The agency should show a backlog of ideas ranked by expected effect and effort, then report what each test taught you, including the ones that did not win. Our guide to growth marketing consultants covers the individual version of this role.

When to hire one

Situation	Fit
You have customers, a repeatable sale and a clear unit of value	Good fit. There is something to optimise
You have no product market fit yet	Poor fit. Fix the product and the offer first
You have no tracking and no data	Fit after a measurement setup, which the agency can do first
Your team is strong and has capacity	Use a consultant for direction instead
You need a specialist skill such as paid search	A specialist agency may serve better

How the fees are built

Monthly retainer

A fixed fee for a team and a set of hours or deliverables. It gives the agency stability to plan and gives you a predictable cost. Check what is in scope, how many experiments run each month and who the named people are.

Retainer plus performance

A lower fixed fee plus a share tied to a metric you both trust, such as revenue from a channel. The metric must be measured in your own system, defined in the contract and capped or reviewed if it is open ended.

Project fee

A fixed fee for a defined piece of work, such as a funnel audit or a new onboarding flow. Good for a first engagement.

Media spend

Paid media spend is separate from the fee. Pay the platforms from your own accounts where possible, so the money and the data stay with you.

The brief to give

1. The business model, who buys and why, and your current numbers.
2. The one number to move, the date and the value of reaching it.
3. The budget for fees and for media.
4. What has been tried and the results.
5. The systems the agency can touch and the ones it cannot.
6. Who on your side approves work and how quickly.

A tight brief produces a proposal you can compare. Ask each agency for a 90 day plan against the same brief and compare the plans, not the credentials.

Questions to put to the agency

• Who will work on my account, and what else are they working on?
• Show a past test log with wins and losses, with client details removed if needed.
• How do you prioritise experiments?
• Which tools do you use and who pays for them?
• What access do you need, and how do you hand it back?
• What would you not do for a business like mine?

Walk away from any agency that promises a specific revenue figure up front. A responsible agency commits to a method, a pace and a transparent report, and to reaching a target by way of tests that can be checked. See also our test for the claim in award winning agency language.

The first ninety days

Days 1 to 30: measure and map

Tracking is audited and fixed. The funnel is mapped with real numbers at each step. A shortlist of biggest gaps is agreed with you. You should see a baseline report.

Days 31 to 60: first tests

Two to four experiments run on the biggest gaps. Each has a hypothesis, a success measure and a run time. You should see test results, including any that failed, and what the agency learned.

Days 61 to 90: scale what worked

The winning changes are rolled out. The next round is chosen using what the first round taught. You should see a movement in at least one funnel step, and a plan for the next quarter.

If after ninety days you have a better dashboard, a clear test record and at least one validated improvement, the engagement is on track. If you have only a presentation, ask what changed on the site or in the campaigns.

Keep ownership

All accounts, tracking, creative and data should sit in your name. The agency works within them. At the end, you keep the test log, the dashboards and the learning. That record is what you are really buying. For the landing page work that often features early in an engagement, see our guide to landing page agencies.

When growth runs through an assistant

A growth agency measures the funnel it can see: clicks, sessions, sign ups and sales. A growing number of buyers start somewhere that funnel does not record, by asking an assistant for the best option in your category. They read one composed answer, and the first sign of your business is a mention in it, or its absence. That step happens before any session your analytics can count.

Add it to the agency's scope as a measured channel. Choose the questions your buyers ask, put them to ChatGPT, Gemini, Perplexity, Claude and Google AI Overviews each month, and record whether you are named and which sources are cited. AI Knows Us automates that measurement and lists the sources behind each answer, so a growth agency can set a baseline and test changes against it just as it does for any other channel.

Questions about hiring a business growth agency

How much does a growth agency cost?

It depends on team size and scope. Ask for a fixed monthly fee against a written scope, and compare proposals on the same brief.

How long should I commit?

Choose a three to six month initial term with a review at ninety days. Growth work needs time for tests to run.

Is a growth agency the same as a marketing agency?

No. A marketing agency often delivers channels and creative. A growth agency is organised around a metric and a testing cadence.

Can I hire one for a small business?

Yes, if there is a product that sells and enough traffic or leads to test on. For lower volumes, a consultant may suit better.

What should the report show?

The baseline, the experiments run, the results, the learning and the next steps.