Part-Time FD Hidden Costs: What to Watch For

A part-time FD engagement involves more costs than the headline retainer fee suggests. VAT, travel expenses, additional project fees, platform charges, and scope creep can all add to the total cost of an engagement — sometimes significantly. Knowing what to expect and what to negotiate before you sign prevents budget surprises and protects the commercial relationship from unnecessary friction.

This article sets out every additional cost you should investigate before committing to a fractional FD arrangement, and how to address each one clearly in your contract.

VAT: The Cost Most Businesses Overlook

Fractional FD services supplied by a VAT-registered provider are subject to VAT at the standard rate of 20%. A £2,500 monthly retainer therefore costs £3,000 including VAT. If your business is VAT-registered and makes taxable supplies, you can reclaim the input VAT on your next VAT return, making the net cost equal to the quoted fee. However, businesses that are not VAT-registered — including many smaller SMEs, charities, and businesses below the £90,000 registration threshold — cannot recover this VAT and must budget for the full VAT-inclusive amount.

Travel and Expenses

Remote-first engagements have become the norm since 2020, and many fractional FDs deliver the majority of their work without requiring on-site presence. However, board meetings, team sessions, and significant milestone events often benefit from or require physical attendance. Travel and subsistence costs for these visits are typically recharged to the client at cost.

Before signing, clarify:

• How many on-site visits per month are expected within the standard retainer, if any
• Whether travel time counts against the committed day allocation or is absorbed by the FD
• What expense policy applies — mileage rate (HMRC advisory rates are 45p per mile for the first 10,000 miles), train fare class, hotel policy for overnight stays
• Whether expenses require pre-approval above a certain value

For a primarily remote engagement, expenses are typically modest — under £200 per month in most cases. For businesses requiring regular on-site presence, particularly those outside major cities, travel costs can add meaningfully to the effective monthly cost.

Additional Days Above the Retainer

A retainer commits to a fixed number of days per month. When business demands exceed that allocation — a fundraise approaches, an acquisition emerges, or a financial crisis requires intensive involvement — additional days are required and billed at an agreed day rate. This rate is typically the FD's standard day rate and should be documented in the engagement letter before work begins.

Businesses often underestimate how quickly additional days accumulate in an active period. A fundraise requiring four weeks of intensive support can easily generate 10–15 additional days of FD time beyond the retainer, adding £8,000–£15,000 to the period's cost. Budget for this contingency proactively.

The scope creep risk

Scope creep occurs when the FD's involvement gradually expands beyond the agreed retainer scope without formal renegotiation. This is not necessarily bad — it often reflects the FD adding genuine value — but it can create billing disputes if not managed transparently. Ensure your engagement letter clearly defines the scope and includes a mechanism for agreeing additional work in writing before it begins.

Platform or Matching Fees

If you engage a fractional FD through a specialist platform like FractionalFD, there may be a platform fee charged to the business, to the FD, or incorporated into the quoted rate. Understanding how the platform fee is structured matters for comparing like-for-like costs between a platform-introduced FD and one sourced directly.

Platform fees typically cover matching, vetting, contract infrastructure, dispute resolution, and replacement guarantees. These services have real value — particularly the replacement guarantee, which protects you if the engagement does not work out. Weigh the platform fee against the cost of sourcing, evaluating, and contracting directly, which is rarely as free as it appears.

Specialist Third-Party Costs Incurred on Your Behalf

A fractional FD may identify the need for specialist third-party input — a tax adviser, a corporate lawyer, a financial modelling specialist, or a sector-specific consultant — in the course of their work. These costs are incurred separately from the FD's fees and are your responsibility unless the engagement letter specifies otherwise.

Common third-party costs that a fractional FD engagement may generate include:

• Legal fees for reviewing or drafting facility agreements, shareholder documents, or employment contracts
• Tax advice from a specialist tax partner for R&D tax credit claims, EIS/SEIS structuring, or business sale tax planning
• Actuarial advice for defined benefit pension obligations
• Financial modelling or data analysis support for complex scenarios

A good FD will flag these requirements proactively and obtain quotes before costs are committed. A reactive approach to third-party costs — where invoices arrive without prior discussion — is a governance failure that should be addressed immediately.

Onboarding and Initial Setup Time

The first month of a fractional FD engagement typically involves a higher level of activity than subsequent months, as the FD gets to grips with your business, finance systems, team, and existing obligations. Some engagements bill this separately as a setup or onboarding fee; others absorb it within the first month's retainer. Either approach is reasonable, but it should be explicit in the engagement letter.

Expect the first month to involve:

• Review of prior year accounts, management accounts, and board packs
• Meetings with key team members across finance, operations, and leadership
• Assessment of the existing finance function capability and systems
• Identification of priority issues and a 90-day action plan

IR35 and Employment Status Considerations

Since the IR35 off-payroll working rules were extended to medium and large private sector businesses in April 2021, businesses engaging fractional FDs need to assess the employment status of the engagement correctly. If the engagement falls inside IR35, the business (as the end client) bears responsibility for deducting income tax and National Insurance contributions before paying the FD, substantially increasing the effective cost.

Most genuinely fractional FD engagements — where the FD works for multiple clients, provides their own equipment, and operates with genuine autonomy — fall outside IR35. However, this assessment must be made correctly on a case-by-case basis, ideally with support from an employment tax adviser. FractionalFD provides guidance on IR35 status assessments as part of the engagement setup process.

"IR35 is the cost most businesses forget to model. Getting it wrong doesn't just create a tax liability — it changes the economics of the entire engagement."

How to Protect Yourself Against Unexpected Costs

The most effective protection against unexpected costs is a clear, detailed engagement letter that addresses each of the items above before work begins. Specifically, your engagement letter should define:

1. Whether fees are quoted exclusive or inclusive of VAT
2. The expense policy and any pre-approval thresholds
3. The day rate for additional days above the retainer
4. The process for authorising third-party costs
5. Whether an onboarding fee applies in month one
6. The IR35 status determination methodology

For a complete picture of what a retainer agreement should contain, read our guide on what is included in a monthly FD retainer fee. For a view of total costs in context, see our article on how much a part-time FD service typically costs.