A fractional CTO can usually appear in an SBIR budget as a consultant, but generally cannot be the Principal Investigator, because SBIR rules require the PI to be primarily employed by the small business, meaning more than half of their working time, at the time of award and during the project. In Phase I the small business is also typically expected to perform about two-thirds of the work, measured by budget, so consultant and subcontractor costs together are capped at roughly a third. Plan the proposal around a PI who is genuinely on your payroll, and put the fractional CTO where the rules allow: advising on architecture, reviewing technical risk, and helping write the technical plan.
This question comes up with deep-tech and research-heavy founders more than any other group I work with. They have a promising technical idea, a small team, and a federal grant that could fund a year of development without dilution. The natural instinct is to name the most senior technical person they know as PI. If that person is a part-time adviser, the proposal has a structural problem before anyone reads the science.
What follows is how I think about the budget and roles. It is not legal or grants advice, the details differ between agencies, and every solicitation sets its own rules, so read the one you are applying to line by line.
The two rules that shape the budget
The PI must be primarily employed by your company
Federal SBIR rules have long required that the Principal Investigator's primary employment be with the small business at the time of award and for the duration of the project. Primary employment is defined as more than half of the person's time. Agencies such as NSF describe it as 51 percent. The rule is about employment, not about project hours: the PI does not have to spend half their time on this one project, but more than half of their working time has to be with your company.
A fractional CTO who splits their week across several clients will almost never meet that test with you. Even if they could, being named PI on a federal award while also advising other companies invites questions you do not want during review.
Most of the Phase I work has to be done in-house
For Phase I, the small business is generally expected to perform at least two-thirds of the research or development effort, measured by budget. In Phase II that drops to at least half. Consultants, subcontractors and other outside costs share what is left. Some agencies allow deviations with approval, but you should not build a proposal that depends on one.
That ratio is the main constraint on how much fractional CTO time you can fund through the grant.
Where a fractional CTO fits
Within those limits there is a sensible role, and it is often valuable.
As a named consultant
Most agencies allow consultant costs with a short letter of commitment and a rate. A fractional CTO listed as a consultant for a defined number of hours on architecture, security and technical risk review is normal. Keep the hours realistic and tie them to specific tasks in the work plan, because reviewers do read budgets.
Before the proposal is submitted
The most useful time to involve senior technical judgment is usually before you write the technical objectives. A good adviser will push on whether the milestones are measurable, whether the plan depends on infrastructure you do not have, and whether the Phase I scope is honest about what can be proven in the time. That work is paid by the company, not the grant, but it often decides whether the grant is won.
Bridging into the commercial build
SBIR funds research and development toward a product. The parts that are not research, such as building the production platform, hiring the first engineers, and choosing vendors, still need technical leadership. A fractional CTO funded outside the grant can own those decisions while the PI owns the funded research. I have written about the wider question of how to budget for technical leadership at this stage.
A worked budget example
Here is an illustrative Phase I shape, not a template. Suppose the proposal budget is 300,000 dollars.
To meet the two-thirds rule, at least 200,000 dollars needs to be costs incurred by your company: salaries for the PI and employees, fringe, your own overhead, and so on. That leaves up to 100,000 dollars for everything external. If you also need a university subcontract for testing at 60,000 dollars, a fractional CTO consultant line has to fit, together with any other outside services, inside the remaining 40,000 dollars.
That is still meaningful senior time over six to twelve months, as long as it is focused on reviews and decisions rather than hands-on building. If your plan needs more outside engineering than that, the rules are telling you the company does not yet have the in-house capacity the program expects. The answer is usually to hire, not to stretch the consultant line.
Common mistakes I see
- Naming a part-time adviser or a university professor as PI without checking the primary-employment rule.
- Budgeting an agency or contractor team to do most of the build, which breaks the in-house work ratio.
- Writing technical objectives that describe a product launch rather than a feasibility question.
- Treating the grant as runway for general engineering, then struggling to show progress against the funded objectives.
- Assuming last year's rules still apply. The programs lapsed in late 2025 and were reauthorized in spring 2026 with changes, so check the current solicitation.
Getting the structure right early
The cleanest setup I have seen is simple. A founder or early hire who is full-time at the company is PI. The fractional CTO is a modest consultant line in the budget and, separately, a paid adviser to the company on everything the grant does not cover. Both are clear about which hat they are wearing in which meeting.
If you are planning an SBIR application and want a second view on the technical plan and how senior help fits around it, you can book a call. The how it works page explains what a fractional engagement covers, and I have also written about how fractional CTO fees interact with the R&D tax credit, which raises some related questions.
FAQ
Can a fractional CTO be the PI if they work more than half their time for us?
If they are genuinely employed by your company for more than half of their working time, they may meet the test, but at that point they are closer to a part-time employee than a fractional adviser. Check the agency rules and get grants advice before naming them.
Does the 51 percent rule mean the PI must spend half their time on the project?
No. It concerns their employment with the company, not hours on this project. Agencies set separate minimum effort levels for the PI on the project, which vary.
Can grant money pay for the fractional CTO to help write the proposal?
Generally no, because proposal preparation happens before the award. Pay for that work from company funds.
Is STTR different?
Yes. STTR requires a formal partnership with a research institution and allows the PI to be primarily employed by that institution. The work split rules are also different, so read the STTR solicitation separately.