Fixed Price vs Time and Materials: Which Contract to Use?

Quick answer: In fixed price vs time and materials, a fixed price contract charges one agreed total for a defined scope, so the seller carries overrun risk. A time and materials (T&M) contract bills actual hours at set rates plus materials, so the buyer carries the risk, often limited by a not-to-exceed cap. Choose fixed price for clear scope, T&M for uncertain scope.

The contract type you choose shapes how you quote, how you track work and how you invoice. Get it wrong and you either work for a fraction of your rate or lose the client over a surprise bill. This guide compares fixed price and time and materials contracts side by side, runs the same project through both models with real numbers, and shows how T&M contract invoicing and fixed fee invoicing look in practice. Either way, you can produce the invoices with our free invoice generator.

Fixed price vs time and materials at a glance

Factor	Fixed price	Time and materials
Price	One agreed total	Hours multiplied by rate, plus materials
Who carries overrun risk	Seller	Buyer (seller above any cap)
Best when scope is	Clear, stable, well documented	Uncertain, evolving, exploratory
Budget certainty for client	High	Low without a cap
Profit upside for seller	Higher if you work efficiently	Capped at your hourly margin
Admin effort	Upfront scoping, change orders	Timesheets, receipts, regular reporting
Typical invoicing	Milestones or deposit and balance	Weekly or monthly, hours and costs itemized
Main dispute risk	What is in or out of scope	Whether hours were necessary

What is a fixed price contract?

A fixed price (or fixed fee, lump sum) contract sets a single price for a defined deliverable. The client knows the total before work starts, and you are paid that total whether the job takes 80 hours or 160. Fixed price works well for repeatable, well-understood work: a five-page brochure website, a bookkeeping catch-up of a known number of months, a standard installation.

The key documents are a detailed scope and a clear change process. A statement of work sets out deliverables, assumptions, exclusions and acceptance criteria. When the client asks for something outside it, you price it separately with a change order rather than absorbing it.

What is a time and materials contract?

A time and materials contract bills the client for actual labor at agreed hourly or daily rates, plus the actual cost of materials and expenses. The US Federal Acquisition Regulation describes it as acquiring supplies or services on the basis of direct labor hours at specified fixed hourly rates (covering wages, overhead, general and administrative costs and profit) and materials at cost, and says it may be used only when it is not possible to estimate accurately the extent or duration of the work. It also requires a ceiling price that the contractor exceeds at its own risk (see FAR 16.601, time-and-materials contracts). Private contracts are not bound by the FAR, but the same logic is a good model for small businesses.

T&M suits discovery work, troubleshooting, renovations where you cannot see behind the walls, ongoing support and any project where the client expects to change direction. For a freelancer with no material costs, T&M is essentially hourly billing; our guide to invoicing for hourly work covers timesheets and rate presentation.

Not-to-exceed caps

A not-to-exceed (NTE) amount turns open-ended T&M into something a client's finance team can approve. You bill actual time and materials up to the cap. If you approach it, you warn the client early and either stop, agree a higher cap, or finish at your own cost. Track the running total on every invoice so nobody is surprised.

Worked example: one project, two contract types

A freelance developer is asked to rebuild a client's website. She estimates 120 hours at her rate of $95 an hour: 120 multiplied by $95 = $11,400 of labor.

• Fixed price quote: she adds a 15% contingency for risk: $11,400 multiplied by 1.15 = $13,110.
• T&M quote: $95 an hour for actual hours, plus licences and stock images at cost, with a not-to-exceed cap of $13,000 on labor.

Now look at three possible outcomes for actual labor hours:

Actual hours	T&M labor bill	T&M bill with $13,000 cap	Fixed price	Effective rate on fixed price
105	$9,975	$9,975	$13,110	$124.86/hr
120	$11,400	$11,400	$13,110	$109.25/hr
140	$13,300	$13,000	$13,110	$93.64/hr

Check the figures: 105 multiplied by $95 = $9,975; 140 multiplied by $95 = $13,300, which the cap reduces to $13,000. On the fixed price, $13,110 divided by 105 = $124.86, divided by 120 = $109.25, and divided by 140 = $93.64 an hour.

The lesson: if she works efficiently, fixed price pays her far more per hour. If the job overruns, fixed price still beats capped T&M slightly here only because the contingency was larger than the cap; at 160 hours the fixed price would fall to about $81.94 an hour ($13,110 divided by 160). For the client, T&M is cheaper unless the project overruns significantly. That trade-off is the whole decision.

How the invoices look

Fixed price, invoiced by milestone (40% / 30% / 30%):

• Invoice 1, on signing: 40% of $13,110 = $5,244.
• Invoice 2, design approved: 30% of $13,110 = $3,933.
• Invoice 3, site launched: 30% of $13,110 = $3,933.
• Total: $5,244 + $3,933 + $3,933 = $13,110.

Each invoice names the milestone and shows the contract total and amounts previously billed. Our guide to milestone payments covers schedules and wording.

T&M, invoiced monthly. In October she logs 52 hours and buys a plugin licence for $180 and stock images for $240, both billed at cost:

Line	Qty	Rate	Amount
Development, October 1 to 31 (timesheet attached)	52 hrs	$95.00	$4,940.00
Plugin licence, at cost	1	$180.00	$180.00
Stock images, at cost	1	$240.00	$240.00
Total			$5,360.00

Check: 52 multiplied by $95 = $4,940; $4,940 + $180 + $240 = $5,360. In the notes she adds: "Labor billed to date: $4,940 of $13,000 not-to-exceed; remaining $8,060." ($13,000 minus $4,940 = $8,060.) Materials are listed separately so the client can match them to receipts; see reimbursable expenses on an invoice for how to present pass-through costs. In our invoice generator, each of these is simply a line item with a quantity and rate, and the notes field carries the cap tracking.

Which contract type suits which work?

Type of work	Usual fit	Why
Brochure website from a template	Fixed price	Scope is predictable and repeatable
Bug fixing on an unfamiliar codebase	T&M	Effort is unknown until the problem is found
Kitchen renovation with known layout	Fixed price with allowances	Most work is defined; allowances cover finishes
Repairs behind walls or floors	T&M with cap	Hidden conditions make estimates unreliable
Monthly bookkeeping	Fixed monthly fee	Volume is stable from month to month
Catch-up bookkeeping for messy records	T&M or fixed after review	State of records is unknown until reviewed
Strategy or discovery workshop	Fixed price	Time-boxed with a defined output
Ongoing support and small changes	T&M or retainer	Requests vary and arrive over time

The pattern is consistent: the more predictable the work, the more sense a fixed price makes, and the more hidden or changing the work, the safer time and materials becomes for both sides.

How to choose: a 6-step decision process

1. Rate scope clarity. Can you list every deliverable and acceptance criterion today? If yes, fixed price is viable. If not, lean T&M.
2. Check your estimating history. If your past estimates for similar work were within 10% to 15% of actuals, you can price fixed fees confidently.
3. Ask about the client's budget process. Some clients need a fixed number to get approval; offer T&M with a cap if scope is uncertain.
4. Assess change risk. Many stakeholders, new technology or unclear requirements mean frequent changes, which suit T&M.
5. Price the risk. If you choose fixed price, add contingency in proportion to uncertainty, and write exclusions.
6. Consider a hybrid. Paid T&M discovery, then fixed price for the defined build, then T&M support.

T&M contract invoicing best practices

• Bill on a short cycle. Weekly or monthly invoices keep the client informed and protect your cash flow.
• Itemize roles and rates. If several people work on the job, list each role's hours separately.
• Attach timesheets. Clients approve faster when they can see what the hours covered.
• Separate materials from labor. State whether materials are at cost or include a markup. Our article on the labor and materials invoice shows the standard layout.
• Show the running total against the cap on every invoice.
• Number invoices consistently. A simple sequence from an invoice number generator makes it easy for both sides to track a long engagement.

Fixed price invoicing best practices

• Take a deposit. A first payment on signing reduces risk and confirms commitment.
• Tie each invoice to an objective milestone that the client can verify, such as "design approved in writing".
• Show progress: contract total, this invoice, previously billed and remaining balance.
• Bill change orders separately so the base contract total stays clean.
• Do not track hours only for the client. Track them for yourself, so you know your real effective rate and can price the next fixed bid better.

Managing the risks of each model

Fixed price risks

• Underestimating. The single biggest risk. Break the work into tasks of no more than a day or two each, estimate each, and compare with past actuals before adding contingency.
• Vague acceptance criteria. If "done" is not defined, the client can keep requesting tweaks within the fixed fee. Define the number of revision rounds and what counts as sign-off.
• Client delays. Waiting for content, approvals or access extends the timeline and ties up your capacity. Include a clause that lets you re-schedule or bill a restart fee if the client causes a long delay.
• Front-loaded costs. If you buy materials or subcontract early, make sure the first milestone payment covers them.

Time and materials risks

• Client budget anxiety. Without a cap or regular updates, clients worry about an open-ended bill. Send a short weekly summary of hours used and hours remaining against the estimate.
• Disputes over efficiency. The client may question whether hours were necessary. Detailed timesheet descriptions ("migrated 42 product pages, fixed image paths") answer that before it is asked.
• Hitting the cap early. Warn the client when you reach around 75% of the not-to-exceed amount, with a forecast of the remaining work, so they can approve more budget or reduce scope.
• Lower upside. Your income is limited to hours worked. Review your rate regularly, especially as your speed improves.

Clauses to include in either contract

Whichever model you choose, these terms prevent most billing disputes:

• Scope and assumptions, or for T&M, the estimated scope the hours are based on.
• Rates for each role, plus how materials are charged (at cost or cost plus a stated markup).
• Invoicing schedule: milestones for fixed price, weekly or monthly for T&M.
• Payment terms such as net 15 or net 30, and any late fee your local law allows.
• Change process: how new requests are priced and approved in writing.
• Cap and notification rules for T&M, including when you will warn the client.
• Termination: what is owed if either side ends the contract early, usually work completed to date plus committed materials.

Putting these in a short contract or statement of work takes an hour and saves far longer arguing over an invoice later.

Beyond fixed price and T&M

Two other models are worth knowing. Cost plus bills actual costs plus a fixed fee or percentage; see our sibling guide to cost plus pricing. Value-based pricing sets the fee by the result's worth to the client rather than by hours or costs; see value-based pricing. Ongoing work is often sold as a monthly retainer, which behaves like a fixed price for a fixed block of time. If you are setting hourly rates for T&M work from scratch, our guide to consulting rates covers how to benchmark them.

Create your project invoice. Whether you bill fixed price milestones or monthly time and materials, our free invoice generator lets you itemize hours, materials and milestones, track amount paid and balance due, and download a professional PDF. For a clean look, try the agency invoice template.