When to Hire In-House vs Work With an Agency

The in-house-versus-agency question is usually framed as ideological rather than economic. Founders and CMOs have strong instincts about which is "right". Agencies are for companies that haven't committed to growth yet, or agencies are for companies that know the value of specialists, or in-house teams are for companies that take growth seriously, or in-house teams are overhead you only add once you've earned it. All of these framings contain partial truths and miss the actual question, which is what specific capability needs to exist, at what scale, under what level of ongoing investment, and which delivery mechanism fits best for this particular combination.

This article is the honest decision framework. Written from the side of the business making the decision rather than from the side of an agency selling services, even though NBT is an agency, and the framework will sometimes point at "hire in-house" as the right answer for specific situations.

Why The Question Is Usually Framed Wrong

Three patterns that produce ideological rather than practical decisions.

"Agency is the stepping stone to in-house." The narrative that agencies are what you use until you can afford in-house. This framing assumes in-house is always better and agencies are the lesser option. The reality is that some capabilities genuinely work better as ongoing agency relationships even at scale (certain specialist channels, time-boxed project work, capability areas where external perspective adds value). Treating agency as a placeholder for in-house produces bad decisions in both directions.

"In-house is cheaper at scale." The assumption that headcount eventually costs less than agency retainers. This is true for some capabilities and false for others. A full-time paid media specialist costs £60-90k plus tooling, management overhead, and the cost of empty chairs when they leave. An agency retainer covering the same capability might be £40-70k per year with no hiring cost, no management overhead, and no replacement risk. The maths only favours in-house when the capability is core enough that the other benefits matter more than the cost comparison.

"Agency lacks commitment." The concern that agencies won't care about your business the way in-house people will. Sometimes true, sometimes not. Varies more by specific agency and relationship than by the in-house-vs-agency choice itself. Agencies that structure engagements around outcome accountability (as discussed here) often care more about specific results than in-house teams on flat salaries.

The Capability-by-Capability Framework

The useful decision framework treats each growth capability as a separate decision rather than making one big in-house-vs-agency call. Different capabilities fit different delivery models.

Four questions applied to each capability identify the right fit.

Question 1: Is this capability strategic or executional?

Strategic capabilities (the ones that shape the direction of the business) generally benefit from in-house ownership. Positioning, ICP definition, commercial strategy, pricing, core product marketing. These capabilities require deep context, ongoing relationship with the business, and decision authority that's hard to delegate externally. Even when agencies help with these, the final ownership needs to sit inside.

Executional capabilities (the ones that run tactics against a defined strategy) can reasonably sit with agencies or in-house, depending on the other questions. Paid media execution, SEO content production, specific channel management, technical implementation.

The rough pattern: strategy in-house (at least the owner of it), execution wherever delivers it best.

Question 2: How specialised is the required skill set?

Highly specialised capabilities (deep expertise in specific platforms or disciplines) often fit better with agencies. LinkedIn Ads optimisation at expert level, complex SEO technical auditing, conversion-rate optimisation specialism, specific industry niche knowledge. The expertise required takes years to develop and you need enough volume to justify a full-time specialist. Agencies carry the specialists across many clients; in-house teams either hire one underutilised specialist or hire generalists who don't reach the same depth.

Moderately specialised capabilities (important but learnable) often fit in-house. A mid-level paid media practitioner who needs to be good but not world-class. A content writer who knows your business deeply. These roles grow with the business and produce compound value in-house because they accumulate context over time.

Question 3: Is the workload steady or spiky?

Steady workload (ongoing work that consumes predictable time) fits either model, with in-house often slightly favoured at sustained scale.

Spiky workload (project-shaped demand or seasonal intensity) almost always fits better with agencies. Hiring in-house for spiky demand produces either underutilisation (expensive) or capacity crises (worse). Agencies scale up and down around specific projects without that friction.

Specific examples of spiky work that usually should be agency: website redesigns, brand refreshes, major campaign launches, pitch deck development, event-specific content sprints.

Question 4: Does external perspective add or subtract value?

External perspective adds value for capabilities where challenge and outside view improve outcomes. Strategic diagnostics where the team is too close to the business to see clearly. Positioning work where internal consensus has drifted into blind spots. Competitive analysis where internal knowledge doesn't extend to competitors' reality. For these, agency delivery isn't just operationally equivalent to in-house. It's strategically superior because the external perspective is part of the value.

External perspective subtracts value for capabilities that require deep ongoing context. Founder-adjacent strategic work. Customer-specific account management. Anything where the work needs to know your team, your culture, and your specific dynamics deeply. These belong in-house.

Specific Capability Recommendations

Applying the framework to common B2B growth capabilities gives rough defaults that work for most Series A to Series C companies.

In-house by default: Head of Growth, Head of Sales, VP of Marketing, Marketing Operations/RevOps, product marketing, customer success, sales development (at scale). These roles need ongoing context, strategic ownership, and integration with the broader team.

Agency or hybrid by default: Paid media execution, SEO content production, creative production, website development, specific technical specialisms (martech implementation, advanced analytics, conversion optimisation). These roles benefit from specialist depth that's hard to justify as a full-time hire at most growth-stage company sizes.

Genuinely situational: Content strategy and editorial lead, brand strategy, PR and comms, specific campaign work. These can work either way depending on the specific company's scale, culture, and leadership.

The practical implication: most growth-stage B2B companies end up with a hybrid model. Strategic leadership in-house, specialist execution through agencies, and a judgement call on the middle layer depending on specific circumstances.

What Changes The Decision At Different Stages

Stage matters for some capabilities even when the framework gives a clear default answer.

Seed to Series A: Agency-heavy usually works. The business can't afford senior in-house specialists yet, the workload is often spiky, and external perspective helps the founder see past their own assumptions. The exception: Head of Growth or senior marketing leadership, if the founder isn't filling that role themselves.

Series A to Series B: Hybrid model as described above usually fits. Enough scale to justify some in-house specialists, enough variability to benefit from agency flexibility, enough strategic ambition to want strong in-house leadership.

Series B to C and beyond: More in-house, but not fully. Specialist agency relationships often continue through all stages because specific capabilities never justify in-house specialists at the required depth. The companies that go fully in-house at scale usually over-hired and underutilise the team, or they ended up building an internal agency structurally indistinguishable from buying agency services externally.

When Agencies Fail The Decision Framework

Worth being honest: sometimes the right answer is that a given capability doesn't fit any agency, only in-house. Situations where agencies genuinely can't deliver what's needed.

Deep product knowledge (agencies can't hold the nuance of a complex product the way in-house people can). Customer-specific account strategy (agencies can't do account ownership for your enterprise relationships). Highly regulated or sensitive work (compliance and legal implications often require in-house ownership). Genuinely strategic decisions where the decision-maker needs to be inside the company, not retained externally.

If a capability needs any of these, agency isn't the right answer regardless of other factors in the framework.

Where This Sits in the NBT Growth Model

The in-house-vs-agency question is implicitly a Stage 2 Formulation question. It shapes how the Route gets executed. The team-building at £3M ARR piece covers the in-house side of this decision; this piece is the complement that addresses when to use agencies for specific capabilities.

The honest summary from an agency's perspective: an agency relationship earns its place when it provides specialist depth, external perspective, or spiky-workload flexibility that in-house can't match economically. An agency relationship fails when it substitutes for strategic leadership that should be in-house or when it's selected ideologically rather than by fit to the specific capability need.

If you're wrestling with specific in-house-vs-agency decisions and want an honest outside read on your situation, or you're building a growth team and unsure which capabilities belong inside versus through partners, get in touch for a strategy call. We'll walk through the capability-by-capability view for your specific setup.