The contract type on a proposal is often treated as a sales decision, whichever term the client prefers or whichever format wins the deal faster. It is also an accounting decision. Fixed-fee and time-and-materials engagements are billed differently, recognized differently on the books, and carry the margin risk in different places. A firm that grows without being deliberate about which structure it is using on which engagement tends to find out the difference the hard way, usually on the project that ran long.
What Each Structure Actually Is
Time-and-materials (T&M). The client is billed for actual hours worked at agreed rates, plus any materials or pass-through costs. Revenue tracks effort. If the engagement takes longer than expected, the firm generally bills for the additional time, assuming the client has not capped it with a not-to-exceed clause.
Fixed-fee. The client is billed a set amount for a defined scope of work, regardless of how many hours it actually takes the firm to deliver it. Revenue is fixed at the outset. If the engagement takes longer than estimated, the firm absorbs the additional hours at its own cost.
The difference is not just billing mechanics. It is where the risk of a project running over sits. On T&M, that risk sits mostly with the client’s budget. On fixed-fee, it sits entirely with the firm’s margin.
Revenue Recognition Differences
T&M revenue is generally recognized as work is performed and hours are logged, whether or not the invoice has gone out yet. A firm invoicing monthly for the prior month’s hours still has income earned in the days worked before the invoice is issued, and that unbilled amount is a real asset on the books (unbilled work in progress) even before it becomes an invoice.
Fixed-fee revenue is recognized differently depending on how the engagement is structured. A single short deliverable might be recognized on completion. A longer fixed-fee project is more often recognized on a percentage-of-completion basis, tracking progress against the total scope rather than waiting for a single completion date or booking the full fee the moment the contract is signed. Booking the entire fixed fee as revenue at signing, before any of the work is delivered, misstates the period the revenue actually belongs to.
This distinction matters most at a fiscal year-end that falls in the middle of a project. A firm with several fixed-fee engagements spanning the year-end needs a defensible basis for how much of each fee has actually been earned as of that date, not just how much has been invoiced or collected.
Where the Margin Risk Sits
A T&M engagement protects margin by design: more hours means more revenue, roughly in line with cost, as long as billing rates are set correctly relative to what the firm pays or the opportunity cost of the consultant’s time. The main risk on T&M is scope disputes over whether specific hours were properly billable, not margin erosion from the engagement itself running long.
A fixed-fee engagement inverts this. The firm estimated the hours at proposal stage, priced the fee against that estimate, and now owns the gap if the estimate was wrong. A fixed-fee project that was scoped at 200 hours and actually takes 280 has effectively cut the firm’s realized hourly rate by 30%, and that shows up as compressed margin on that specific project, not as a billing problem the client will help absorb.
This is why the estimating process behind a fixed-fee quote deserves the same scrutiny as the accounting behind it. An underpriced fixed-fee engagement does not become visible as a problem until the project is well underway and the hours have already been spent, at which point there is no billing mechanism left to recover the gap. Tracking actual hours against the original estimate throughout the engagement, not just at completion, is what gives a firm early warning that a fixed-fee project is running over before the full margin is gone.
Scope Creep Is a Different Problem on Each Structure
On T&M, scope creep mostly self-corrects: additional client requests generally translate into additional billable hours, assuming rates and terms are clear. The commercial friction is explaining a growing bill to the client, not absorbing unbilled cost.
On fixed-fee, scope creep is a direct margin threat. Work added to the engagement without a change order is work the firm delivers at no additional revenue, on top of a fee that was already priced against a fixed estimate. A change order process, documented and priced before the additional work starts, is what keeps a fixed-fee engagement’s actual scope matched to what was actually priced. Firms that treat change orders as an administrative afterthought, handled informally after the work is already done, tend to find that fixed-fee projects consistently run over margin in ways that are hard to trace back to a specific cause.
Bookkeeping Implications
Running a mix of fixed-fee and T&M engagements, which is normal for a growing consulting firm, means the books need to track revenue recognition at the project level rather than applying one method across all client billing. Practically, this means:
- Project or class tracking in QuickBooks Online that separates each engagement, whether T&M or fixed-fee, so revenue recognized can be reviewed project by project.
- A defined method for recognizing fixed-fee revenue (completion basis or percentage-of-completion) applied consistently, not chosen after the fact based on which answer looks better for a given period.
- Tracking of unbilled T&M work in progress at period-end, so income earned but not yet invoiced is captured in the right period.
- Actual-hours-versus-estimate tracking on fixed-fee projects, reviewed during the engagement rather than only at completion.
This structure is the same project-level discipline covered in project profitability for small consulting firms, applied specifically to the point where contract type changes how and when revenue lands on the books.
Related Guides
- Project profitability for small consulting firms covers the broader margin-tracking structure this guide’s project-level revenue recognition feeds into.
- Subcontractor expenses for IT consulting firms covers how subcontractor cost is tracked against the same projects, on either contract type.
- Client reimbursements, pass-through costs, and disbursements covers a related billing mechanics question: how pass-through costs are handled once a project structure is in place.
Scope of This Guide
This guide covers the accounting and margin-tracking differences between fixed-fee and time-and-materials contract structures for IT consulting firms. It does not cover:
- Legal contract drafting or change order language, which should be reviewed with a lawyer
- Pricing strategy or rate-setting methodology
- GST/HST or QST registration mechanics, covered in the GST/HST and QST guides in the compliance chapter
This is general information, not advice for a specific engagement or contract. A CPA reviewing your firm’s actual project mix and billing structure can confirm which revenue recognition method fits your specific engagements.