Understand how a cost plan develops from early feasibility to tender, what changes the budget, and when a quantity surveyor can help you make decisions.
A construction cost estimate forecasts the likely cost of a defined building scope using the information available at a particular time. A cost plan develops that forecast from feasibility through concept design, design development and pre-tender, helping you keep the design, budget and expectations aligned.
We recommend starting before major design decisions are locked in, then updating the plan as drawings, site information and the construction programme develop. Early estimates need broad allowances; later estimates use measured quantities and clearer specifications. Each version should explain what is included, what remains uncertain and what has changed.
What should a construction cost estimate tell you?
A useful estimate gives you a basis for a decision, whether that is testing feasibility, choosing a design or going to tender. It should identify the drawings used, the pricing date, the assumed location and programme, and the scope being priced.
Construction cost planning adds an ongoing process: we allocate the budget across building elements, test options and track changes. Our guide to preparing a construction cost plan explains that relationship in more detail.
We also separate the building works from the overall project budget. Land, consultants, authority charges, finance, loose furniture and other owner costs may sit outside the construction estimate. The report should state their treatment and whether GST is included, so the same allowance is neither missed nor counted twice.
What are the stages and typical accuracy ranges?
Accuracy improves as the scope becomes clearer, but a stage name alone tells you little about the quality of the information. The following are broad, typical industry guide ranges for reasonably defined building projects, not guaranteed tolerances or a universal Australian standard.
They vary by project, procurement approach, market conditions and unresolved risks. We assess uncertainty against the stated scope and pricing assumptions; a later scope change is different from an estimating error.
Order of cost: testing feasibility
At this stage, we may have a brief, approximate floor area, intended use and basic site information. We use comparable building costs, adjusted for location, quality and timing, to test whether the proposed scale is broadly affordable.
Accuracy is often described as within plus or minus 20 to 30 per cent at order of cost stage. Complex sites or poorly defined projects can fall outside that range, so feasibility should test less favourable outcomes as well as the central estimate.
Concept: comparing design options
Concept drawings allow us to examine the layout, building form and major elements such as structure, external walls and services. We can compare options before the team spends time detailing a design that exceeds the budget.
A broad guide is plus or minus 15 to 20 per cent. Unresolved ground conditions, services requirements or finish selections can still materially affect the result.
Design development: checking the coordinated design
Architectural, structural and services information now supports more detailed measurement and pricing. We replace broad allowances with defined quantities and identify gaps between consultants’ documents.
A typical guide range is plus or minus 10 to 15 per cent, depending on documentation and risk. We use this review to resolve budget pressure before completing the tender package.
Pre-tender: checking readiness for the market
The pre-tender estimate uses the coordinated drawings, specifications and proposed procurement arrangements. It provides a final budget check and a benchmark for reviewing returned tenders.
A commonly used guide is plus or minus 5 to 10 per cent where documentation is complete and conditions are reasonably stable. Contractor workload, competition and qualifications can still produce tenders outside that range; the estimate is not a guaranteed offer to build.
What drives the total cost?
The total depends on more than floor area. A compact building on an accessible site can have a different cost profile from a similarly sized building with complex geometry, difficult excavation or restricted deliveries.
We work through five connected drivers:
- Quantities: the measured or assumed extent of the works, including foundations, structure, finishes, services and external works. Changes in area, height or layout can affect several elements together.
- Rates: the cost of labour, materials, plant and subcontract work, adjusted for specification, location and productivity. Site establishment, supervision, contractor overheads and margin also need clear treatment.
- Contingency: an allowance for uncertainty within the agreed scope. We connect it to identified risks and distinguish design development uncertainty from construction risks where appropriate.
- Escalation: an allowance for expected price movement between the estimate’s base date and the relevant procurement or construction period. It depends on timing and market evidence, rather than a permanent standard percentage.
- Exclusions: items outside the estimate, such as owner-supplied equipment or separate enabling works. An exclusion still needs an owner and a budget elsewhere if the project requires it.
Contingency and an accuracy range serve different purposes. Contingency is an allowance within the budget; the accuracy range describes uncertainty around the estimate and should not automatically be added as another allowance.
Who needs a cost plan, and when?
Anyone committing resources to a building project benefits from understanding the cost before decisions become expensive to reverse. We tailor the report to the decision and the organisation using it.
- Developers need early feasibility advice before committing to a site or design, followed by updates as the scope and delivery strategy develop.
- Owners need a realistic budget before detailed design, especially for renovations where existing conditions can influence the work.
- Builders can use cost plans during early involvement to test buildability, packaging and procurement options alongside their own estimating.
- Councils use cost advice when planning and funding their own facilities. For applicants submitting a development application, the required cost report and calculation basis should be checked with the relevant authority.
- Lenders may request independent cost advice when assessing construction funding. We confirm their reporting requirements because a general design cost plan may not meet a particular lender’s brief.
Our cost planning and DA report services cover these different reporting purposes. Establishing the purpose first helps avoid using a report for a decision it was not prepared to support.
How does a quantity surveyor prepare the plan?
We begin with the brief, budget, drawings, specifications, site reports and intended programme. Missing information becomes a recorded assumption or query, rather than disappearing into an unexplained total.
Next, we measure the available information and organise the costs into building elements or trade packages. We select relevant cost evidence, adjust it for the project and check significant items against comparable work or supplier and subcontractor input where appropriate.
We then review risk allowances, escalation and the boundary between construction costs and other project costs. A report prepared by a Certified Quantity Surveyor should make those assumptions understandable, alongside the estimate date and document revisions.
A published average for a building cost estimate in Australia can be a useful starting point. We bring that figure back to your location, site access, specification and delivery programme, because those details decide whether the comparison is useful.
Worked example: how can the budget change between stages?
Consider a hypothetical project with an approved construction budget represented by 100 per cent. Every proportion below uses that same original budget as its denominator; these are illustrative allocations, not recommended contingency or escalation rates.
At concept stage, the estimated works, including preliminaries and contractor margin, take up 85 per cent. Design and construction contingency accounts for 10 per cent, and escalation accounts for 5 per cent, bringing the forecast to 100 per cent.
During design development, measured quantities and updated specifications raise the works component to 92 per cent. Better information supports reducing contingency to 8 per cent, while escalation remains 5 per cent. The forecast is now 105 per cent of the approved budget.
We show that movement before the design proceeds further. Simplifying the roof and rationalising finishes reduces the works component by 5 percentage points of the original budget, bringing it to 87 per cent and the total back to 100 per cent.
At pre-tender, we recheck all components against the final documents and programme. The saving comes from documented design decisions; simply removing the remaining contingency would leave the risks unfunded.
How do we keep the plan useful as design changes?
Each revision should reconcile the previous forecast with the new one. We separate scope changes, quantity changes, rate movements, escalation and changes to risk allowances so the team can see why the total moved.
We agree review points at design milestones and update sooner when a major decision affects cost. A change register records the proposed change, its cost effect, approval status and whether it has been included in the current plan.
We also test value over the building’s intended use. A cheaper finish or services system may bring higher maintenance, energy or replacement costs; our guide to life cycle costing explains how to compare those consequences alongside the initial budget.
How should the plan support tender decisions?
Before tender, we check that the estimate and tender package describe the same scope. Clear tender documentation helps builders price consistent requirements and makes returned offers easier to compare.
When tenders arrive, we review exclusions, allowances, alternatives and programme assumptions as well as the headline totals. An apparently lower offer may omit work included elsewhere, so we reconcile those differences before assessing the budget position.
If tenders exceed the plan, we investigate the cause and assess scope options before recommending changes. For advice about your contractual obligations or a dispute, speak to your lawyer.
Frequently asked questions
Can I get a cost plan before the design is finished?
Yes. We can start with a brief and early drawings, provided assumptions and uncertainty are clearly recorded, then refine the plan as the design develops.
Is a construction cost estimate the same as a builder’s quote?
No. An estimate forecasts likely cost for stated assumptions, while a builder’s quote offers a price for a particular scope subject to its terms, exclusions and conditions.
How much contingency should I allow for a building project?
There is no percentage that suits every project. We assess design completeness, site conditions, delivery arrangements and remaining risks, then review the allowance as those risks change.
