Agency vs in-house: the real cost comparison founders never actually do

Most founders make the agency versus in-house decision based on a surface comparison: the agency retainer versus a single salary. On that basis, in-house usually looks cheaper. The comparison is almost always wrong.

The real cost of building an in-house marketing function capable of doing what a full-service growth agency does is significantly higher than most founders model when they make the decision to hire internally.

A well-structured growth marketing agency brings a team. A senior strategist who has run this process many times before. Someone managing the paid channels. Someone doing the creative and copy. Someone analysing the data and building the attribution model. Someone coordinating the execution across channels.

To replicate that capability in-house, a company typically needs a Head of Growth or senior marketing lead, a performance marketer, a content and copy resource, and a data analyst as a minimum. In some contexts, a designer and a PR function as well.

A senior growth lead in London at Series A costs between 80,000 and 120,000 in salary alone. Add employer national insurance contributions, pension, benefits, equipment, software tools, and the cost of the hiring process itself, and the all-in cost of a single senior hire typically lands between 110,000 and 160,000 per year before they have run a single campaign.

A performance marketer at mid-senior level adds another 55,000 to 75,000 all-in. A data analyst adds 50,000 to 70,000. A content resource adds 40,000 to 60,000. By the time a company has assembled a team capable of genuinely doing full-funnel growth marketing, the annual cost is often between 300,000 and 500,000 in people costs alone, before any media spend or tooling.

A top-tier growth agency engagement for a Series A company typically costs between 8,000 and 20,000 per month depending on scope, which is 96,000 to 240,000 annually. The comparison is not always in favour of the agency, but the honest comparison is agency cost against the full cost of building equivalent internal capability, not against a single salary.

In-house wins when the company has found a repeatable, scalable acquisition model and needs to execute reliably against it over a long period. Deep product knowledge, institutional memory, and the ability to coordinate closely with product and engineering are genuine advantages of internal teams.

In-house also wins when the volume of work is high enough that an agency engagement would require significant overhead in briefing, coordination, and review. At a certain scale, the internal team becomes more efficient simply because of proximity.

An agency wins when the company is still figuring out what works, when the breadth of capability needed exceeds what a single hire can provide, and when speed of learning matters more than depth of execution. It also wins when the company does not yet have the management capacity to hire, onboard, and develop a marketing team without significant distraction from other priorities.