Use hourly billing when effort is uncertain, fixed fees when outcomes and boundaries are clear, and retainers when the client needs continuing access or a recurring capacity commitment.
The best model is not the one with the highest headline price. It is the one that assigns scope and utilization risk to the party best able to control it.
Decision table
| Factor | Hourly | Fixed fee | Retainer |
|---|---|---|---|
| Scope certainty | Low | High | Recurring or variable within boundaries |
| Revenue predictability | Low to medium | Medium | High |
| Margin risk | Client carries time risk | Provider carries delivery risk | Provider carries utilization risk |
| Administration | Detailed time records | Milestones and change control | Capacity, rollover and renewal tracking |
| Best fit | Discovery, support, uncertain work | Defined deliverables | Ongoing advisory or production |
Hourly billing
Hourly protects the provider when the work cannot be estimated reliably. It is easy to explain and difficult to scale because revenue remains tied to time.
Hourly price floor = loaded hourly cost / (1 – target gross margin).
If loaded cost is 60 and the target gross margin is 40 percent, the price floor is 60 / 0.60 = 100 per hour. Loaded cost includes salary or contractor cost, employment costs and a reasonable delivery overhead allocation.
Define what is billable, the rounding increment, approval threshold and reporting cadence. A weekly time summary prevents the client discovering a month of effort at invoice time.
Fixed-fee billing
A fixed fee sells a defined result, not unlimited effort. It rewards efficiency and exposes weak scoping.
Fixed fee = estimated loaded cost + risk allowance + target profit.
A project expected to cost 6,000, with a 15 percent risk allowance and 30 percent target margin on price, needs more than 8,700. Solve price as (6,000 + 900) / 0.70 = 9,857.
Attach assumptions, exclusions, client responsibilities, revision limits and a change process. Fixed price without fixed boundaries is hourly work with the clock hidden from the client.
Retainer billing
A retainer reserves access, capacity or a recurring output. It improves cash flow only when the service boundary is clear.
Choose one model:
- Access retainer: payment reserves availability and response time.
- Capacity retainer: payment includes a defined number of hours or units.
- Deliverable retainer: payment covers a repeating package of outputs.
State whether unused capacity expires, rolls forward or converts to credit. Unlimited retainers invite unlimited interpretation.
A practical selection test
- Can you describe completion in objective terms?
- Can you control the dependencies that determine effort?
- Does the client value speed or simply want access?
- Would a delay create a loss you cannot price?
- Is demand recurring enough to reserve capacity?
Clear completion and controllable dependencies point to fixed fee. Unknown effort points to hourly. Recurring demand and valuable access point to a retainer. A project can combine them: fixed discovery, milestone implementation and a support retainer.
Billing each model in Invoice Crowd
Use time tracking to turn approved billable logs into invoice lines, estimates and proposals for fixed scope, and recurring invoices for a repeating retainer schedule. Keep delivery data even for fixed fees, because actual hours reveal whether the price produced the intended margin.
Frequently asked questions
Which billing model is most profitable?
None automatically. Fixed fees can reward efficiency, hourly protects uncertain effort, and retainers improve predictability. Profit depends on price, scope control, utilization and delivery cost.
How do I calculate an hourly rate?
Divide loaded hourly cost by one minus the target gross margin. A loaded cost of 60 with a 40 percent target margin gives a 100 price floor because 60 divided by 0.60 equals 100.
How do I price a fixed-fee project?
Estimate loaded delivery cost, add a risk allowance, then divide by one minus the target margin. Pair the price with written assumptions, exclusions, revision limits and change control.
Do unused retainer hours roll over?
Only if the agreement says so. Expiry protects reserved capacity, rollover feels fair to clients, and limited rollover can balance both. State the cap and expiry date explicitly.
Can one client use more than one model?
Yes. A common structure is fixed-fee discovery, milestone implementation, hourly out-of-scope work and a recurring support retainer. Separate each boundary in the agreement and invoice.
Should I track time on fixed-fee work?
Yes internally. The client may not be billed by the hour, but actual loaded time is needed to measure project margin, improve estimates and spot scope creep.
