Both ship growth work, but they do not solve the same problem. The honest answer depends on whether your bottleneck is execution capacity (agency) or senior judgement (fractional CMO). Often the right answer is both: a fractional CMO setting priorities while an agency executes inside that framework.
The trade-offs are concrete. This is the comparison founders should be making before signing anything.
Recommended for the post-PMF founder-led buyer
| Dimension | Agency | Fractional CMO |
|---|---|---|
| Who's in the seat | Account manager + junior team | Senior operator (10+ years), embedded |
| Scope | Defined channel: paid, SEO, content, outbound | Whole GTM system: ICP, positioning, channels, conversion, reporting |
| Strategy ownership | Founder still owns it | Operator owns it, founder makes the calls |
| Reporting | Activity dashboards (clicks, impressions) | Pipeline, conversion, payback, what to scale/stop/fix |
| Decision-making | Brand-safe best practice | Opinionated, contextual to your company |
| Speed | Slower: agreed scope, change orders | Faster: embedded operator, no handoffs |
| Typical cost | £6–20k/month + retainer | £5–7.5k/month, 3-month minimum |
| When it's right | You already have a CMO and need execution capacity | You don't yet have a CMO and growth needs senior judgement |
Pick an agency when…
Pick a fractional CMO when…
The fractional CMO sets priorities, channel rules, and reporting; the agency executes a specific channel inside that framework. The CMO runs the agency relationship instead of the founder. That's frequently the cleanest setup for £1M–£20M ARR teams.
Often yes. The fractional CMO sets priorities, channel rules, and reporting; the agency executes a specific channel inside that framework. The CMO runs the agency relationship instead of the founder. That's frequently the cleanest setup for £1M–£20M ARR teams.
The monthly ranges overlap: £5–7.5k for a fractional CMO, £6–20k for a typical agency. But you're buying different things. The agency runs a channel; the fractional CMO runs the system. Most agency engagements still need someone senior to direct them, and that's the role the fractional CMO fills.
3 to 9 months typically. The first 90 days build the diagnosis, operating rhythm, and first system. After that, it's either scale, hand off to internal hires, or move to a lighter advisory cadence.
Also worth reading: Fractional CMO vs. full-time CMO · Fractional CMO cost (UK) · Full Fractional CMO scope · WSS consultancy comparison
Last updated: 11 July 2026