A few weeks into the engagement, your fractional CTO says the thing you half expected: "To move faster on this, I want to bring in one of my engineers." It makes sense. They know people, the people are good, and you need hands. Then the question lands: who pays for that engineer, and at what rate? Is it inside the retainer you already agreed, or a new line on the invoice with a markup you have not seen yet?
The direct answer: the engineer is almost always a separate, additional cost, not something baked into the fractional CTO's retainer. That is normal. What you need to nail down is the rate, whether there is a markup, and who the engineer actually answers to. Get those three things in writing before anyone starts, because this is where a clean engagement quietly turns into an agency relationship you did not sign up for.
Why the engineer is a separate cost
Your fractional CTO's retainer buys their time and judgment, not a team. When they bring in an engineer, that is additional labor at additional cost, and expecting it to come free inside the existing retainer is not realistic. A fractional CTO reserving two days a week for you at $18,000 a month is not also absorbing a full-time engineer out of that number.
So the engineer is a new cost. The real questions are about how that cost is structured, because there are two very different models and they have very different implications for you.
Pass-through. The engineer bills you at their actual rate, and the fractional CTO takes nothing on top. You pay what the engineer costs, full stop. The fractional CTO's incentive to add people stays clean, because they make nothing from headcount. This is the model you want.
Markup. The fractional CTO bills you for the engineer at a rate above what they pay the engineer, and pockets the spread. Say the engineer costs them $70 an hour and they bill you $110. That $40 is margin. This is how agencies work, and it is not inherently dishonest, but it changes the incentive in a way that matters: now the person advising you on whether you need more engineers makes money every time the answer is yes.
That conflict is the whole reason to care about this. You hired a fractional CTO partly to get an honest read on how much building you actually need. The moment they earn a margin on every engineer they place, that honesty is compromised, even if they are a good person. You want the advice on headcount coming from someone who is neutral on headcount.
What to pin down before anyone starts
Three things, in writing, before the engineer writes a line of code.
The rate and the markup, stated plainly. Ask directly: "Is this pass-through at cost, or is there a margin? If there is a margin, what is it?" A straight operator will tell you without flinching. If the answer is vague, or you get a blended team rate with no breakdown, that is a signal to slow down. You are entitled to know whether you are paying for an engineer or for an engineer plus a finder's fee.
Who the engineer reports to, and who carries the risk. If the engineer is technically a subcontractor of your fractional CTO, then IP assignment, confidentiality, and quality are the fractional CTO's responsibility to guarantee, and your contract should say so. If the engineer contracts directly with you, that responsibility is yours to manage. Neither is wrong, but you need to know which one you are in, because it determines who you call when the work is late or the code is bad. This is the same who owns your code question that bites founders after the fact.
What happens to the engineer when the fractional CTO leaves. If your fractional CTO winds down but the engineer they brought is now load-bearing, can that engineer stay? On what terms? An engagement where all the hands are the fractional CTO's subcontractors, on the fractional CTO's paper, can leave you with nothing when the engagement ends. Agree up front that any engineer embedded in your product can convert to a direct relationship with you if you want them.
The line between a fractional CTO and an agency
Here is the trap. It starts with one engineer, pass-through, clean. Then it is two. Then the fractional CTO suggests a small markup "to cover management overhead." Then you look up and you are paying a blended team rate to a group of people who all work for your fractional CTO, and the person deciding how big that team should be is the person billing you for it. You now have an agency, priced like an agency, with none of the guardrails you would have negotiated if you had known you were hiring one.
There is nothing wrong with a fractional CTO who can bring a team. It is often exactly what you need, and a good one placing a great engineer at cost is a gift. The problem is only the silent drift from advisor to vendor. Keep it clean by keeping the two things separate in your head and in the contract: the fractional CTO is paid for judgment, and any engineers are a distinct, transparent, at-cost line you can inspect and control. If your fractional CTO is proposing to build a team, it is worth a call to structure the rates and reporting before it grows. You can book a call to talk through the setup, or read how we think about scoping the engagement so the team question is answered before it comes up.
FAQ
Does my fractional CTO's retainer cover engineers they bring in?
No, almost never. The retainer buys the fractional CTO's own time and judgment. Any engineer they add is a separate, additional cost. The important detail is whether that cost is passed through at the engineer's actual rate or billed with a markup.
Is it a red flag if my fractional CTO marks up the engineers?
Not automatically, but it creates a conflict of interest you should see clearly. If they earn margin on every engineer placed, their advice on how many engineers you need is no longer neutral. Ask for the markup to be stated plainly, and prefer pass-through-at-cost so the headcount advice stays honest.
Who owns the code an embedded engineer writes?
It depends on your contract structure. If the engineer is your fractional CTO's subcontractor, IP assignment flows through them and must be spelled out. If the engineer contracts with you directly, it is on your paper. Either way, confirm IP assignment in writing before work starts.
What happens to the engineer when the fractional CTO leaves?
Decide this up front. If an engineer becomes central to your product, agree that they can convert to a direct relationship with you. Otherwise you risk losing all the hands the moment the fractional CTO winds down, even if the engineers were happy to stay.