Article focus: This article explains why Cost to Complete (CTC) is the most important commercial number in construction, how it differs from budget tracking, why contractor and developer CTC forecasts diverge, and why it becomes especially critical in Design & Build projects and in the New Zealand construction industry.
Sources: Flyvbjerg et al.; construction cost-overrun research literature
Construction projects generate enormous amounts of information throughout their lifecycle.
Project teams monitor budgets, procurement commitments, subcontractor payments, labour productivity, progress claims, variations, consultant reviews, council approvals, cash flow forecasts, and programme updates.
Despite this, many projects still experience cost overruns, programme delays, reduced profitability, and funding challenges.
The reason is simple.
Many organisations focus heavily on historical costs while paying insufficient attention to future costs.
This is where Cost to Complete (CTC) becomes critical.
In my experience, Cost to Complete is the most important number in construction because it provides visibility into the future commercial and financial position of a project.
While Quantity Surveyors often prepare and monitor Cost to Complete forecasts, CTC is fundamentally a project finance tool. It provides developers, investors, lenders, contractors, and project teams with visibility into future funding requirements, project risks, and forecast profitability.
Historical costs explain where a project has been. Cost to Complete helps stakeholders understand where a project is going.
More importantly, it provides management with an opportunity to take corrective action before commercial problems become unmanageable.
Cost to Complete represents the estimated cost required to complete all remaining project obligations from the current reporting date until final completion.
In its simplest form:
The purpose of Cost to Complete is not simply to report costs — it is to forecast the future:
This is why Cost to Complete sits at the intersection of construction delivery, commercial management, and project finance.
Many organisations focus heavily on comparing actual expenditure against budget. While budget monitoring remains important, it only reflects historical performance. Cost to Complete focuses on future exposure.
Consider the following example:
| Item | Amount |
|---|---|
| Original Budget | NZD 70,000,000 |
| Actual Cost to Date | NZD 58,000,000 |
| Remaining Budget | NZD 12,000,000 |
At first glance, the project appears healthy. However, a detailed Cost to Complete review identifies:
| Risk Item | Forecast Cost |
|---|---|
| Labour Productivity Losses | NZD 350,000 |
| Extended P&G Costs | NZD 650,000 |
| Consultant Review Delays | NZD 250,000 |
| Council Approval Delays | NZD 300,000 |
| Defect Rectification Allowance | NZD 150,000 |
| Subcontractor Standby Costs | NZD 200,000 |
| Total Additional Exposure | NZD 1,900,000 |
Without an effective Cost to Complete process, management may not identify these risks until the project approaches completion.
This is why Cost to Complete is often considered the most important number in construction.
One of the most misunderstood aspects of Cost to Complete is that different stakeholders often have different Cost to Complete requirements.
The contractor focuses on one key question: how much will it cost to complete the contracted works profitably?
The contractor's Cost to Complete generally includes:
The contractor uses Cost to Complete to forecast final project cost, forecast profit, potential overruns, and commercial risks.
The developer focuses on a different question: how much additional investment is required before the development becomes operational and starts generating revenue?
The developer's Cost to Complete may include:
Although both parties are assessing the same project, their Cost to Complete forecasts can be significantly different.
Cost to Complete forecasting becomes even more important in Design & Build projects.
Under Design & Build procurement models, contractors often carry responsibility for design management, consultant coordination, authority approvals, building consent compliance, construction delivery, commissioning, Practical Completion, and Code Compliance Certificate (CCC) processes.
This creates a significant commercial challenge.
Project completion is not always determined by physical construction progress. In many cases, project completion is heavily influenced by consultant review periods, design approvals, council approval processes, compliance requirements, outstanding documentation, and CCC close-out activities.
A project may be physically 95% complete but still unable to achieve Practical Completion or CCC due to unresolved approval issues.
For this reason, Cost to Complete forecasting must extend beyond construction costs. It must also consider programme risks associated with consultant reviews and regulatory approvals.
One of the biggest lessons learned from large Design & Build projects is that physical progress does not always equal commercial completion.
A building may appear complete. Trades may have finished most of their work. Apartments may be ready for occupation. Yet unresolved consultant reviews, outstanding council requirements, compliance documentation, commissioning issues, or CCC delays can still prevent formal completion — with real commercial consequences for every stakeholder waiting on that milestone.
One of the most underestimated Cost to Complete risks is programme extension. When consultant reviews or council approvals take longer than anticipated, the programme often extends. As a result, Preliminary and General (P&G) costs continue.
These costs may include:
Even when very little physical work remains, these costs continue every week.
In many projects, the largest Cost to Complete risk is not the remaining construction work itself. It is the cost of time.
Programme delays frequently create another major commercial risk: idle resources.
Where approvals remain outstanding, contractors often need to retain site supervisors, defect rectification teams, commissioning specialists, finishing trades, and specialist subcontractors.
Although work output may reduce significantly, labour and subcontractor costs continue. This creates a dangerous situation where project expenditure continues while progress slows.
An effective Cost to Complete forecast must identify these risks early and include realistic allowances for labour and subcontractor exposure.
The New Zealand construction industry has faced significant challenges in recent years including labour shortages, material price escalation, supply chain disruptions, regulatory compliance requirements, consultant resource constraints, and programme uncertainty.
Many projects are delivered under fixed-price Design & Build contracts where contractors carry substantial commercial risk.
Under these conditions, Cost to Complete becomes far more than a reporting exercise. It becomes a critical management tool.
Many project failures do not occur because management lacks information. They occur because warning signs are identified too late.
An effective Cost to Complete process helps identify those warning signs before they become major commercial problems.
Consider a large apartment development. The contractor reports:
| Item | Amount |
|---|---|
| Actual Cost to Date | NZD 65 million |
| Contractor Cost to Complete | NZD 3 million |
| Forecast Final Cost | NZD 68 million |
The physical construction is largely complete. However, the project still requires consultant reviews, compliance close-out, CCC approval, defect rectification, and final commissioning.
The developer's assessment may be:
| Item | Amount |
|---|---|
| Contractor Cost to Complete | NZD 3.0 million |
| Finance Costs | NZD 0.8 million |
| Marketing & Sales Costs | NZD 0.5 million |
| Operational Readiness Costs | NZD 0.4 million |
| Development Overheads | NZD 0.3 million |
| Developer Cost to Complete | NZD 5.0 million |
This demonstrates why developers, investors, and lenders closely monitor Cost to Complete forecasts.
The table below is a quick heat-map of where each risk hits hardest — contractors and developers are rarely exposed the same way.
Notice the pattern: CCC delays, finance costs, and sales delays hit developers hardest, while labour and subcontractor risk sit mainly with the contractor — which is exactly why the two parties need separate CTC forecasts.
Traditional Quantity Surveying focuses heavily on measurement, procurement, contract administration, valuations, and variations. These skills remain essential.
However, modern commercial management increasingly requires Quantity Surveyors to understand forecasting and business performance.
The ability to prepare and challenge Cost to Complete forecasts is one of the most valuable commercial skills a QS can develop.
CTC shifts the QS mindset from reporting historical costs to forecasting future commercial exposure.
A strong CTC process surfaces risks such as consultant delays and P&G overruns before they become unmanageable.
Understanding both contractor and developer CTC needs helps the QS communicate clearly across the project team.
CTC forecasting must account for approvals and compliance, not just remaining physical works.
Mastering CTC transforms the QS role from cost recorder to commercial decision-maker.
It transforms the role from cost recorder to commercial decision-maker.
Many construction professionals focus on budgets. Others focus on actual costs. The most successful commercial professionals focus on forecasts.
Budgets explain what was planned. Actual costs explain what has happened. Cost to Complete explains what is likely to happen.
In Design & Build projects, profitability is not determined solely by construction productivity. It is also heavily influenced by consultant reviews, council approvals, programme extensions, and the resulting Preliminary and General costs.
A project can be physically complete yet continue losing money every week due to approval delays and extended site overheads.
For this reason, Cost to Complete should never be treated as a simple accounting exercise. It is a strategic forecasting tool that sits at the heart of project finance, commercial management, and construction delivery.
Projects rarely fail because management lacks information. They fail because future risks are identified too late and are not reflected in the Cost to Complete forecast.
That is why Cost to Complete remains the most important commercial number in construction.