Capped fixed-fee accountant: how to avoid overruns

Quick answer. A capped fixed fee blends instalments paid during the year, based on an estimated scope, with a year-end true-up if actual volume exceeds the assumptions. Because accounting fees have been freely set since Decree no. 2012-432, any overrun must be covered by a written clause in the engagement letter.

A fixed fee is not a promise of a frozen price whatever happens. It is a global price built on a defined scope and volume assumptions. When real activity diverges from those assumptions (more entries, exceptional transactions, late document delivery), the fixed fee can be trued up at year-end. The issue is almost never the principle, but the lack of written framing. Many business owners discover an additional fee at closing without ever understanding what triggered it.

At Hayot Expertise, a firm led by a chartered accountant registered with the Ordre des experts-comptables of Île-de-France and a statutory auditor, we regularly see competing engagement letters that stay silent on this point. This guide explains the mechanism, the real causes of overruns, and the clauses that make the invoice predictable.

The capped fixed fee is a hybrid model. It combines two building blocks. First, a provisional fixed fee, paid as instalments spread over the year (usually monthly), calculated from a contractual scope and volume assumptions. Second, a year-end true-up that adjusts fees if the work actually performed exceeded the planned scope.

French chartered accountants set their fees freely. The profession's Code of ethics, codified in articles 141 to 169 of Decree no. 2012-432 of 30 March 2012, sets no scale: fees are set by contract, in the engagement letter. It is precisely this freedom that makes clause drafting decisive. A well-written capped fixed fee protects both parties; a poorly written one turns the closing into a tense negotiation.

This model should not be confused with the underlying choice between fixed fee and time spent. To understand what distinguishes these two billing logics, you can compare the fixed fee and time-based billing. The capped fixed fee is in fact a third path, borrowing the fixed fee's predictability and the time-based model's fairness when activity surges.

Yes, and it is normal when the actual scope diverges from contractual assumptions. The fixed fee pays for defined work: a volume of entries, a number of filings, a compilation engagement on the accounts. If reality exceeds that scope, the extra work is by construction not covered by the initial fee.

The key nuance: a legitimate overrun assumes the cause falls outside the contractual scope. A firm cannot true up because it underestimated its own fixed fee. It can do so because the client assigned, during the year, unplanned work, or because actual volume surged. The line between these two situations must be drawn in writing, upfront.

Common causes of an overrun#

The quality and regularity of document delivery weigh heavily. Smooth bookkeeping often runs through a tool like Pennylane to streamline bookkeeping and a connected business account such as Qonto: less re-keying, fewer missing documents, therefore less to true up.

Instalments smooth cash flow for both the firm and the client. Rather than a single heavy year-end invoice, the client pays regular amounts matching a provisional fixed fee. The true-up then follows, upward or, more rarely, downward.

Here is the typical sequence of a well-run capped fixed fee:

1. Scope definition in the engagement letter: included engagements, estimated entry volume, covered filings, expected deliverables.
2. Provisional fee calculation split into instalments (monthly or quarterly), with their collection calendar.
3. Monitoring during the year: a checkpoint helps detect a volume gap early and alert the client before closing.
4. Gap assessment at closing: comparison between actual scope and contractual scope.
5. True-up: invoicing of the additional amount (or credit note) under the revision clause, after informing the client.

The mid-year checkpoint is the link many firms forget. Yet it is what turns a bad surprise into a shared decision. To place this mechanism within a full engagement, bookkeeping and review work form the base on which the fee is calibrated.

An additional fee reflects, in a correct capped fixed fee, real work above contractual work. The most frequent reasons are an entry volume overrun, a one-off engagement outside recurring accounting, or rework tied to incomplete documents. Transparency here is an ethical duty: Decree no. 2012-432 requires the professional to inform the client.

The cost of self-management gone wrong#

A well-framed additional fee remains far below the cost of bookkeeping or filings that go off track. Tax penalties are set by law and stack with the late-payment interest.

These surcharges stack with the late-payment interest. Set against a true-up fee, they show where the real financial risk lies. This is one of the core arguments for structured support, in line with tax support for the business owner.

It all depends on the written scope, and this is where misunderstandings arise. A bookkeeping fee may include periodic VAT returns, the preparation of annual accounts and the tax return package, or only part of these. The golden rule: anything not listed in the engagement letter is not in the fee.

To avoid the blind spot, you should decode each line of an accountant's quote before signing. An unplanned monthly VAT return, an added payslip, an extra income return: all lines that, if absent from the scope, will trigger a perfectly legitimate true-up that nonetheless feels like a surprise.

The capped fixed fee is not a trap; it is the most honest model when a company's activity is variable. The frozen fixed fee suits everyone as long as nothing moves; the moment a client triples its invoice volume or adds an activity, either the firm absorbs the loss (and quality eventually suffers), or it renegotiates mid-stream. The capped fixed fee settles this dilemma by setting the rule at signing.

The underestimated risk, in the files we take over, is almost never the true-up rate: it is the total absence of a written threshold. An engagement letter that mentions a true-up at actuals without defining the reference scope or the trigger threshold leaves a grey zone. The client feels they have a fixed fee, the firm reasons on time spent, and the closing becomes friction ground. The fix is not to flee the model, but to demand quantified assumptions.

The pure fixed fee suits stable, predictable activity, where volume varies little year to year. Time spent suits one-off engagements or highly uncertain situations. The capped fixed fee is the right compromise for a growing or seasonal business that wants visibility without paying a safety margin on a volume it may never reach.

In practice: the anti-overrun checklist#

• Require a precise written scope: included engagements, covered filings, deliverables.
• Have volume assumptions quantified (number of entries, payslips, filings).
• Check for a true-up trigger threshold.
• Ensure no out-of-scope service is invoiced without prior written approval.
• Ask for a mid-year checkpoint to detect gaps early.
• Explicitly list excluded engagements (sale, tax audit, holding structuring).
• Frame the document delivery calendar and urgency deadlines.
• Confirm whether VAT and the tax return package are included or billed separately.

This discipline applies from year one. For an owner just starting out, we detail the first year of engagement after incorporation, the period when volume assumptions are hardest to set.

Liberal professions and micro-entrepreneurs switching to the standard regime face a calibration challenge: the volume of their first structured year is inherently poorly known. A capped fixed fee with a six-month checkpoint beats a pure fixed fee set too low that will end up renegotiated.

Companies subject to a compilation engagement must separate recurring bookkeeping from the compilation engagement itself. To clarify this scope, the difference between compilation and bookkeeping is a useful prerequisite: what the fee covers depends on the level of engagement chosen.

Electronic invoicing changes the volume equation. All VAT-liable businesses must be able to receive structured electronic invoices from 1 September 2026, regardless of size; issuance will apply to large companies and mid-caps on 1 September 2026, then to SMEs and micro-enterprises on 1 September 2027. Configuring and supporting this transition is often a service outside the recurring fee: better to anticipate it in the engagement letter than to discover it in a true-up.

We support this compliance work as part of our accounting engagement, framing upfront what falls within the fee and what constitutes a separate engagement.

Recently, a services SME owner reached out to us after a closing experienced as a cold shower: a sizeable additional fee, on a fee he believed was closed. Reviewing his engagement letter, the finding was clear-cut: no volume assumption, no threshold, just a passing mention of a possible true-up. His invoice volume had doubled in a year, the real work followed, but nothing made it predictable.

We rewrote the framework: quantified scope, trigger threshold, half-yearly checkpoint, list of excluded engagements. The following year there was no surprise, because a gap spotted mid-year was discussed in time. The lesson is consistent: the model was not at fault, the contract was.

Hayot Expertise advice. Before signing, systematically ask for three things: the exact scope in included engagements, quantified volume assumptions, and the precise true-up mechanism with its threshold. A serious firm has no reason to refuse this transparency, which is moreover an ethical duty. It is the best antidote to the surprise invoice.