Fractional CTO for Series A/B Startups: Scaling Tech Leadership

You've raised your Series A. Maybe even Series B. Growth is accelerating. The engineering team that got you here is straining under the pressure. And you're wondering: do we need a full-time CTO now, or can a fractional CTO help us scale?

This guide is for founders navigating the specific challenges of post-Series A growth—when the stakes are higher, the team is bigger, and the technology decisions have more significant consequences.

Why Series A/B Is Different

The fractional CTO discussion at Series A/B differs fundamentally from earlier stages:

At Pre-Seed/Seed:

Small team (2-5 engineers)
Technical decisions affect product
Focus on building the right thing
Budget-constrained

At Series A/B:

Growing team (10-30+ engineers)
Technical decisions affect organisation
Focus on building things right at scale
Budget available but ROI expected

The complexity isn't just about more code or more features—it's about more people, more process, and more coordination overhead. What worked at 5 engineers breaks at 20.

The Specific Challenges at Series A/B

1. Team Scaling

You're not just hiring developers anymore. You need:

Team leads and managers who can handle people, not just code
Specialists in areas like DevOps, security, or data engineering
Structure that allows teams to work independently
Career paths that retain your best people

The fractional CTO brings pattern recognition: they've seen what works and what fails when scaling from 10 to 50 engineers.

2. Technical Debt Reckoning

The MVP that got you product-market fit wasn't built for scale. Now you face choices:

What technical debt is blocking growth?
What can you live with for another 18 months?
Where do you need to invest in rewrites vs refactors?
How do you pay down debt while still shipping features?

These decisions require experience balancing technical idealism with business pragmatism.

3. Architecture for Scale

Your architecture needs to handle:

10x traffic without falling over
Multiple teams working in parallel without stepping on each other
New products and features without destabilising core functionality
International expansion if that's on the roadmap

The wrong architecture choices now create multi-year technical debt.

4. Process Maturity

Ad-hoc processes that worked at seed stage create chaos at scale:

How do you maintain code quality with 5 teams shipping daily?
How do you make decisions when everyone can't fit in one room?
How do you onboard new engineers without founders doing it personally?
How do you handle incidents when there's no single person who knows everything?

5. Due Diligence and Governance

Series B often brings:

More sophisticated investors asking harder technical questions
Board expectations for technology governance and reporting
M&A interest requiring due diligence readiness
Compliance requirements (SOC 2, GDPR, industry-specific regulations)

What a Fractional CTO Does at Series A/B

At this stage, the fractional CTO role shifts toward:

Strategic Architecture

Designing systems for scale, not just function
Making technology choices that support future growth
Balancing innovation with stability
Creating architecture review processes

Engineering Organisation Design

Defining team structures (squads, chapters, guilds)
Creating role definitions and career ladders
Establishing engineering management practices
Building hiring and interview processes at scale

Technical Operations

Implementing SRE and DevOps practices
Building monitoring and observability
Creating incident response procedures
Establishing security and compliance practices

Executive Functions

Board reporting on technology
Investor relations and due diligence
Vendor negotiations at scale
Technology budget management

Preparing for the Next Phase

Defining what a full-time CTO role should look like
Supporting CTO search if that's the path
Building sustainable practices that work without you
Creating documentation and knowledge bases

When Fractional Still Makes Sense at Series A/B

Despite larger budgets, fractional CTO can still be optimal when:

1. You Have Strong Technical Leads

If your senior engineers or VP Engineering can handle day-to-day execution, you might only need strategic oversight. A fractional CTO provides the CTO-level thinking without duplicating execution capability.

Signs this applies:

Your technical leads are making good decisions
Execution isn't the problem—direction is
You need board-level representation more than daily leadership

2. You're Not Ready for the Full-Time Commitment

Finding and hiring a great full-time CTO takes 6-12 months. A fractional CTO provides coverage while you search—and helps you define exactly what you need.

Signs this applies:

You're not sure what kind of CTO you need
You need help defining the role
Previous CTO searches haven't worked out

3. Specific Phase-Based Needs

Sometimes you need intensive CTO involvement for specific phases:

Pre-Series B due diligence preparation
Major architectural transformation
Rapid team scaling during growth burst
Crisis recovery after technical failure

A fractional CTO can scale up for these periods, then scale back.

4. Budget Optimisation

Even with Series A/B funding, a full-time CTO costs £150-250K+ salary plus equity. If you can solve your problems with 2-4 days/week of fractional leadership plus strong internal managers, the economics might still favour fractional.

When You Should Go Full-Time Instead

Fractional isn't always the answer. Consider full-time CTO when:

1. Technology Is Your Core Differentiator

If your technology is what you're selling—if technical innovation is your moat—you probably need full-time CTO attention.

2. Team Size Exceeds ~25 Engineers

Beyond 25 engineers, the coordination and leadership demands often exceed what part-time can provide. You need someone thinking about the organisation every day.

3. You Need Unified External Representation

Enterprise customers, major partnerships, and some boards expect a dedicated CTO. Part-time leadership might signal insufficient commitment.

4. Internal Political Complexity

If you have strong, competing technical leaders who need mediation and direction, that requires full-time presence and relationship building.

The Hybrid Approach

Many Series A/B companies use a hybrid model:

Fractional CTO + VP Engineering

The fractional CTO handles:

Strategy and architecture
Board and investor communication
Hiring senior roles
Vendor and partnership decisions

The VP Engineering (full-time, internal) handles:

Day-to-day team management
Sprint planning and execution
Individual contributor career development
Technical project delivery

This splits the CTO role into strategic (fractional) and operational (internal) components.

Fractional CTO + Strong Tech Leads

Similar concept, but with tech leads rather than VP Engineering:

Fractional CTO provides strategic oversight
Tech leads manage individual teams
Weekly touchpoints maintain alignment

This works when you have capable tech leads but no management layer.

Making It Work at Series A/B

1. Increase Engagement Level

What worked at seed (2 days/month) won't work at Series A. Plan for:

Series A: 1-2 days/week minimum
Series B: 2-3 days/week or consider full-time

2. Define Authority Clearly

At scale, ambiguity kills. Define:

What decisions the fractional CTO makes vs advises on
Their authority with team leads and managers
Their role in hiring decisions
Their responsibility for budget

3. Integrate Properly

A fractional CTO at Series A/B can't be a peripheral advisor. They need:

Regular team touchpoints
Presence in key meetings
Access to management tools and metrics
Real relationships with senior engineers

4. Plan for Transition

Whether to full-time CTO or to sustained fractional, have a plan:

What triggers the need for full-time?
How will you transition?
What should be documented for continuity?

Case Study: Series A SaaS Company

Situation: B2B SaaS company, £8M Series A, 18 engineers, strong technical founder who was struggling to balance hands-on coding with leadership.

Fractional CTO Engagement (2 days/week):

Month 1-2: Assessment and quick wins
Month 3-4: Engineering org redesign (2 teams → 4 squads)
Month 5-6: Hiring support (2 team leads, 4 senior engineers)
Month 7-8: Architecture for multi-tenancy at scale
Month 9-12: Due diligence prep for Series B

Outcome:

Team scaled from 18 to 32 engineers
Technical founder moved to Chief Product Officer role
Series B closed at 3x valuation increase
Transitioned to full-time CTO hire with fractional CTO advising on search

Cost-Benefit at Series A/B

Fractional CTO (2 days/week)

Annual Cost: £50,000-£100,000 What You Get:

Strategic leadership and architecture guidance
Board and investor representation
Hiring and team structure support
Flexible scaling up/down

Full-Time CTO

Annual Cost: £150,000-£250,000+ (salary + benefits + equity) What You Get:

Daily leadership and presence
Full commitment and availability
Long-term ownership and accountability
Unified external representation

The Question to Ask

"Can our problems be solved with 2-3 days/week of senior leadership, supported by strong internal execution? Or do we need someone thinking about this every day?"

If the former, fractional still works. If the latter, invest in full-time.

Preparing for the Conversation

If you're a Series A/B founder considering fractional CTO support, be ready to discuss:

Current team structure — How is engineering organised today?
Key challenges — What's not working? What's keeping you up at night?
Growth trajectory — How many engineers in 12 months? 24 months?
Internal leadership — Who are your strongest technical leaders?
Decision timeline — What's driving urgency?
Long-term vision — Full-time CTO eventually? Or sustained fractional?

Summary

At Series A/B, the fractional CTO question becomes more nuanced:

Fractional can still work if:

You have strong internal technical leadership
Your needs are strategic more than operational
You're in a specific phase (due diligence, scaling burst)
You're building toward full-time but not ready yet

Consider full-time when:

Technology is your primary differentiator
Team exceeds 25+ engineers
Daily leadership attention is required
External stakeholders expect dedicated CTO

The right answer depends on your specific context—team strength, growth rate, competitive dynamics, and what kind of company you're building.