Construction Contract Types in Australia | From Fixed Price to Cost Plus to EPC & more

When people ask what “type” of construction contract they have, they are usually asking about one thing when they should be asking about three. The label on the front page matters far less than how three separate decisions have been made and whether those decisions line up. For a Contractor, getting them to line up is what keeps you paid, keeps your margin intact, and keeps you out of a dispute you did not need to have.

This guide covers all three decisions behind the common construction contract types in Australia. It starts with the decision that most directly controls your money, then shows you how to choose a structure that works for you rather than one that quietly loads the risk onto your side.

3 Decisions Behind Every Construction Contract Type

Every construction contract in Australia is built from three choices. The first is the delivery method, which decides who carries the design risk and when you as Contractor are brought onto the job. The second is the pricing structure, which decides how your price is calculated and who wears the cost if the job runs over. The third is the contract form, which is the document you sign, whether an Australian Standard, an industry form, or a bespoke contract drafted by the other side.

These three choices have to match. A developing design paired with a fixed price, or a collaborative delivery model paired with a hard Lump Sum, is where a lot of Contractor pain begins. The rest of this guide takes each decision in turn.

1. Pricing Structures and Who Carries the Cost Risk

The pricing structure is the decision most Contractors mean when they talk about construction contract types, because it is the one that hits your bank account. These are the pricing structures used across Australian projects.

Lump Sum (Fixed Price)

Under a Lump Sum contract you agree to complete a defined scope for a single fixed price. It is the most common structure on projects where the design is well advanced and the scope is clear. The price certainty in a Lump Sum protects the Principal, not you.

You carry the risk of your own pricing, your productivity, and cost escalation, and you normally build a contingency into the number to cover it. That certainty only holds while the scope stays still, so Variations, Provisional Sums, and Prime Cost items are where a Lump Sum most often moves against you. A Lump Sum is only as good as the design and scope you priced it against.

Rachelle Hare – In my experience

The Contractors who get burned on Lump Sum are almost always the ones who priced against a design that was only part finished and assumed the rest would be close enough. It rarely is. Before you commit to a fixed number, qualify your tender against the documents you were actually given and price your Provisional Sums honestly rather than optimistically. Then make sure the Variations clause genuinely lets you recover when the scope grows, because a fixed price sitting on a weak Variations regime is a trap.

Schedule of Rates

A Schedule of Rates contract sets agreed rates for defined units of work, such as a rate per cubic metre or per item, and you are paid for the quantities actually measured as the work proceeds. It suits jobs where the kind of work is known but the quantities are not, which is common in civil works, earthworks, remediation, and some fit-outs.

The Principal carries the quantity risk because they pay for what is actually done. You carry the rate risk, so your rates need to cover your real costs and margin across the range of quantities that might turn up. The part that catches Contractors out is administration, because without disciplined measurement and records a Schedule of Rates job becomes very hard to get paid on cleanly.

Cost Plus, Do and Charge, and Time and Materials

Under a Cost Plus contract you are reimbursed for the actual cost of the work, being labour, materials, and plant, plus an agreed margin set either as a fixed fee or a percentage. Do and Charge and Time and Materials arrangements are versions of the same idea, paying your labour at agreed hourly or daily rates with materials at cost. Cost Plus moves most of the cost risk to the Principal, which is why it is used where the scope genuinely cannot be pinned down.

It looks safe from the Contractor’s side because you recover what you spend, but there is a real exposure in two places. The first is disputes over what counts as recoverable cost, so the definition of “cost” and the margin need to be tight and your books need to be genuinely open. The second is the Principal’s ability to keep paying an open ended number, so checking their financial capacity before you start is not optional.

Rachelle Hare – In my experience

Cost Plus feels comfortable because you are recovering your outlay, but a percentage margin quietly rewards you for spending more, and that is exactly the point a Principal will attack when the final account lands. I steer clients toward a fixed fee or a capped margin so your incentive and the Principal’s expectation are pointing the same way. Keep records you would be comfortable handing to an adjudicator, define recoverable cost precisely, and never run Cost Plus for a client whose ability to pay you have not checked.

Guaranteed Maximum Price (GMP)

A Guaranteed Maximum Price contract works like a Cost Plus arrangement with a ceiling. A ceiling, also called a cap, is the most the Principal can be required to pay. You are reimbursed your costs plus a fee up to that ceiling, and if the actual cost comes in higher, you wear the difference. Savings below the ceiling are often shared with the Principal under a gain share mechanism.

GMP is popular where the design is still developing but the Principal wants budget certainty, and it pairs naturally with Early Contractor Involvement or Design and Construct. The word “guaranteed” runs against the Contractor, so the risk lives in the detail. What the ceiling actually covers, whether your qualifications and exclusions hold up, and whether a change in scope lifts the ceiling are the points that decide whether a GMP is workable or whether you have handed the Principal a fixed price wearing a friendlier name.

Target Cost

A Target Cost contract sets an agreed target, and the gap between the target and the final out-turn cost is shared between the parties under a pain share and gain share formula. Beat the target and you share the saving. Exceed it and you share the overrun. These arrangements are common in alliances and collaborative or Early Contractor Involvement projects, and they only work when the target is set with real rigour and the cost records are genuinely open.

Table of Pricing Structures

Project Delivery Methods

The delivery method decides how much design risk you take and when you are engaged. Construct Only keeps design with the Principal and their consultants, while Design and Construct hands the design risk to you. Early Contractor Involvement brings you in early to help shape the design and the price, and Managing Contractor, EPC and EPCM, and Alliance models sit further along the spectrum and change your exposure again.

The pricing structure you agree needs to suit the delivery method, because carrying design risk on a fixed price is a very different proposition to carrying it on a collaborative Target Cost.

We cover each model in detail in our guide to Project Delivery Methods.

Contract Forms

The contract form is the document your pricing structure and delivery method are written into. The common Australian Standards forms are AS 4000-1997 and AS 2124-1992 for Construct Only work, and AS 4902 and the older AS 4300 for Design and Construct, all published by Standards Australia. Beyond the Standards there are ABIC contracts, used where an architect acts as the Superintendent, GC21 for government work, and HIA and Master Builders forms for residential work.

The Standards forms are generally the more balanced starting point, while some industry forms are weighted toward one side. Almost all of them are amended through Special Conditions that can shift risk well away from the printed page, so reading the Special Conditions is where a Contractor earns or loses margin.

Our Guide to Construction Contracts in Australia sets out how to choose between the forms.

The Australian Legal Overlay

Whatever construction contract type you sign, several statutory frameworks sit on top of the contract, and some of them cannot be written out of it.

1. Security of Payment

Every State and Territory has Security of Payment legislation that gives Contractors and Subcontractors a statutory right to progress payments, backed by payment claims, payment schedules, and fast adjudication. It applies regardless of your pricing structure and you generally cannot contract out of it. Used properly, it is one of the strongest tools you have to get paid, so it is worth knowing the timeframes that apply in your jurisdiction.

2. Retention and Security

Retention monies and bank guarantees mean you are effectively financing part of the Principal’s risk, sometimes for the length of the defects liability period well past Practical Completion. On a large project that is real money tied up for a long time. Some jurisdictions now require retention to be held in trust, which is worth knowing when you go to recover it.

3. Unfair Contract Terms

Unfair Contract Terms law under the Australian Consumer Law applies to standard form small business contracts and carries significant penalties. For a smaller Contractor or Subcontractor being handed a one sided head contract or subcontract, this regime can work in your favour. It is a useful point of leverage when you are asked to sign terms that are heavily skewed to the other side.

4. Domestic Building Work

Domestic building work is regulated separately in each State and Territory, with mandatory contract terms, statutory warranties, and insurance obligations. Requirements differ, so a contract that is compliant in one jurisdiction may not be compliant in another.

As one example, in Queensland the QBCC permits Cost Plus for domestic work but strongly recommends legal advice first, given a long history of disputes on that structure.

Other States and Territories take different approaches, so always check the rules that apply where your project is being built.

How to Choose the Right Construction Contract Type

When choosing your Construction Contract Type, it’s important to consider a number of questions and project requirements rather than just take whichever contract type lands on your desk.

Step 1: Start with how complete the design and scope actually are. A finished, well documented design can support a Lump Sum, while an evolving or uncertain scope points you toward Schedule of Rates, Cost Plus, GMP, or Target Cost. Fixing a hard price against unfinished information is one of the ways Contractors can lose the most money on a project.

Step 2: Then work out which risks you can genuinely price and control. If a risk sits outside your control, such as the completeness of someone else’s design, resist a structure that makes you carry it. Match the pricing structure to your delivery method and contract form so all three line up rather than pull against each other.

Step 3: Before you price or sign, read the clauses that move risk back to you. The Variations mechanism, Provisional Sums and Prime Cost items in a Lump Sum, the measurement rules in a Schedule of Rates, and the ceiling definition and exclusions in a GMP are some of the usual culprits. If those clauses are weak, the type of construction contract will not protect you.

Rachelle Hare – In my experience

The Contractors who avoid pricing disputes choose their structure off the state of the design, not off what the Principal would prefer to sign. If the design is not finished, I tell clients to push back on a hard Lump Sum every time. It is far cheaper to negotiate the right structure before you price than to argue your way out of the wrong one after the job has gone sideways.

FAQs about Construction Contract Types

What are the main construction contract types in Australia?

The main construction contract types are usually described by their pricing structure, being Lump Sum, Schedule of Rates, Cost Plus, Guaranteed Maximum Price, and Target Cost. Each one allocates cost risk differently between the Principal and the Contractor. The right choice depends on how well defined the scope is and which risks you are able to price and control.

What is the most common construction contract type?

Lump Sum is the most widely used pricing structure on projects with a well developed design, because it gives the Principal price certainty. Common does not mean right for your job. The best structure depends on how clearly the scope is defined and which risks you as Contractor can actually manage.

Is a Cost Plus contract safer for the Contractor?

It can be, because you recover your actual costs, but the safety is conditional. Your real risks are disputes over what counts as recoverable cost and the Principal’s ability to keep paying an open ended number. Tight definitions, genuinely open books, and a check on the Principal’s financial capacity are what make it work.

What is the difference between a GMP and a Lump Sum?

Both give the Principal a cap on price. A Lump Sum fixes the price up front against a defined scope, while a GMP reimburses your actual costs up to a guaranteed ceiling and often shares any savings below it. GMP suits projects where the design is still developing.

What is the difference between a pricing structure and a delivery method?

The pricing structure decides how your price is calculated and who wears a cost overrun. The delivery method decides who carries the design risk and when you are engaged, such as Construct Only or Design and Construct. They are separate decisions that need to suit each other.

Which construction contract type is best for a Contractor?

There is no single best type, because each one shifts risk in a different direction. The best type for you is the one that matches the completeness of the design and keeps the risks you cannot control off your side of the ledger. Working through the design certainty first is the fastest way to narrow the choice.

Can you change the risk allocation in a standard form contract?

It is possible to change the risk allocation in a standard form contract, and indeed this is very common in Australia. Most standard form contracts are amended through Special Conditions or in-line in an electronic version of the document, and those amendments can move risk a long way from the balanced position in the standard form. This is why it’s important to pay as much attention to the amendments as to the pricing structure and the type of construction contract itself.

Does Security of Payment apply to every construction contract type?

Security of Payment legislation applies to most types of construction contract provided the requirements of the Act are met (eg the site is in that jurisdiction etc). The Act gives you a statutory right to progress payments regardless of whether the contract is Lump Sum, Cost Plus, or any other structure, and you generally cannot contract out of it. The specific process and timeframes vary between States and Territories.

Do construction contract types apply to residential building?

Yes, and residential work carries extra rules in every State and Territory, including mandatory terms, statutory warranties, and insurance. Some structures, particularly Cost Plus, attract closer scrutiny for domestic work depending on the jurisdiction. We recommend that you get the contract reviewed before you commit to one.

Get Your Construction Contract Reviewed Before You Sign

The cheapest risk control available to a Contractor is having the contract checked before you price or sign it. We read the pricing structure, the delivery method, and the Special Conditions together, so the risks you are being asked to carry are clear before you commit.

We offer a fixed fee Construction Contract Review, and where the terms need to change, Construction Contract Negotiation to help you get the amendments you need.