Fractional CTO vs dev agency vs in-house: how to decide

In short: a fractional CTO gives you senior technical judgment for a few days a month. A development agency gives you people who build. An in-house CTO gives you both, full time, at full salary. They answer different problems, and the most expensive mistake is hiring the wrong one for the problem you actually have. This guide explains how to choose, how fractional work is priced, and what the different titles mean.

The three options in one table

	Fractional / virtual CTO	Development agency	In-house CTO
What you buy	Judgment, decisions, oversight	Delivery capacity	Judgment and leadership, continuously
Writes the code	Usually not	Yes	Sometimes
Who they work for	You	Themselves, then you	You
Cost shape	Monthly retainer or fixed scope	Project price or day rates	Salary, equity, recruiting time
Best when	You must decide or supervise but are not technical	You know what to build and need it built	Technology is the product and you are scaling a team

What "fractional", "virtual", "interim" and "tech advisor" mean

The titles overlap and are used loosely. A working distinction:

• Fractional CTO and virtual CTO: effectively the same. A senior technical leader engaged part time, often on a monthly retainer, across one or a few companies.
• Interim CTO: a full-time stand-in for a defined period, usually while you hire or after a departure.
• Tech advisor: advice on request, without owning outcomes or running anything.

Whatever the label, check three things: what decisions they own, how many hours a month that means in writing, and whether they have a financial interest in what they recommend.

How fractional CTO work is priced

I will not quote a market rate; figures circulating online vary by region, seniority and scope. The pricing models are stable:

• Monthly retainer for a defined number of days or a defined deliverable. Predictable, and the most common.
• Fixed-scope engagement for a defined question: an architecture review, a vendor selection, a due diligence.
• Hourly or day rate for ad hoc advice. Flexible, but it rewards slowness and discourages you from calling.

Ask what is included in a month, what happens when you need more, and whether you can stop at the end of any month. My own oversight offer is a rolling monthly engagement with no minimum term; the current range is on the Build Oversight page.

A decision guide

Choose a fractional CTO if

• You have hired an agency you cannot evaluate and want someone on your side to grade the work.
• You face a one-off technical decision (build vs buy, which stack, which vendor) and nobody independent to put it to.
• You need a technical voice in investor or board conversations but not a full-time salary.

Choose an agency if

• The scope is written down, the requirements are ranked and you only need capacity to build.
• Pair the agency with independent oversight if you cannot judge the output yourself.

Choose an in-house CTO if

• Technology is your core differentiator, you are hiring a team, and you need someone present daily.

The combination that fails most often

A non-technical founder, an offshore agency and no independent technical voice. Reporting turns reassuring instead of factual, and the real gap appears at acceptance, when it is expensive. In one build I reviewed, six sprints in on a $90,000 project, every report was green. Graded against the written acceptance criteria, three of the six sprints were only partially delivered: the vendor had been demoing the happy path and deferring error handling, permissions and data migration to a phase that did not exist in the contract. Caught at sprint six, it was renegotiated at no cost. Caught at acceptance, it would have been a change request in the high five figures.

Conflict of interest: the question to ask first

A fractional CTO who also sells development, or takes referral fees from agencies, is not independent of your vendor choice. Ask directly and get the answer in writing. I run delivery at a software agency, so I decline any engagement overseeing a Moroccan agency, and the Digi4 relationship is disclosed in writing before any introduction.

Next steps

If you have a single decision to make, the Architecture Power Hour is one prepared hour with a one-page decision record. If you already have a vendor, Build Oversight grades their work every sprint, in writing. If you are still choosing a vendor, start with how to choose an IT vendor without the project slipping.