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What Is a Prime Cost in Construction Contracts?

Published 26 June 2026 · Last updated 26 June 2026

Quick Answer

A prime cost in construction contracts refers to an allowance for items not yet selected or priced at the time of contract signing. These often include fixtures and fittings where the exact specification is unknown. The allowance covers supply costs only, not installation. It's crucial to manage these costs to avoid budget overruns.

In construction contracts, the term 'prime cost' refers to an allowance set for certain items not yet selected or priced when the contract is signed. Typically, these items are fixtures, fittings, or materials where the exact brand, model, or specification is still to be decided by the client. Importantly, prime cost allowances cover only the supply cost of these items and not their installation.

Under Australian standards, a prime cost item is allocated a specific dollar amount in the contract. This placeholder is a best estimate of the expected cost. However, the final cost may vary depending on the client's eventual selection. This can lead to adjustments in the total contract price once the items are chosen and the actual costs are determined.

A common misconception is that prime cost covers all associated expenses, including installation. However, it strictly pertains to the supply cost. If the chosen item exceeds the allowance, the client must cover the difference. Conversely, if it costs less, the client may receive a credit.

To see how this plays out in practice, consider a contract for a new residential development in Melbourne. Suppose there's a prime cost allowance of $10,000 for kitchen appliances. Once the client finalises their choice of a high-end brand, the actual cost becomes $12,500. The client is responsible for the additional $2,500. If you are operating on a 37% marginal tax rate, these additional costs aren't directly deductible, but they can affect your depreciation schedule and overall project cost.

In our experience reviewing thousands of properties across Australia, we find that prime costs can frequently lead to disputes if not properly understood. Clients often underestimate the actual market cost of high-quality items, leading to budget shortfalls. Moreover, many assume installation is included, resulting in unexpected expenses. Clear communication and realistic budgeting can mitigate these issues.

The answer can differ depending on your situation. For instance, in commercial projects, prime cost items might include advanced technology systems or specialised equipment. In residential projects, they often cover high-end finishes or bespoke fittings. Additionally, the impact of prime costs can vary significantly depending on whether you are working on a fixed-price contract or a cost-plus contract. In cost-plus contracts, the risk of exceeding the allowance is generally lower as the client pays the actual cost of items chosen.

When dealing with prime costs, professional advice is invaluable. A Chartered Quantity Surveyor can provide accurate estimates and help manage these allowances effectively. Collaborating with your accountant ensures that any financial implications, such as tax or depreciation impacts, are fully understood.

  • Review your contract to understand what items are listed as prime costs.
  • Research current market prices for these items to ensure allowances are realistic.
  • Consult with your builder or QS to adjust allowances if necessary.
  • Finalise selections early to avoid last-minute cost surprises.
  • Document any changes to the contract as selections are made.
  • Regularly review costs during the project to manage your budget effectively.
  • Frequently Asked Questions

    Do prime costs cover installation?

    No, prime costs only cover the supply of items. Installation costs are separate and must be budgeted for independently.

    Can prime costs be adjusted?

    Yes, prime costs can be adjusted as selections are finalised. It's important to document these changes to avoid disputes.

    What happens if the actual cost is less than the prime cost?

    If the actual cost is less, the client may receive a credit for the difference, reducing the overall contract price.

    How do prime costs affect tax returns?

    While prime costs themselves are not directly deductible, they can influence depreciation schedules and overall project costs, impacting tax calculations.

    Are there state-specific rules for prime costs?

    While the concept of prime costs is consistent across Australia, specific contract terms and building regulations may vary by state. Consult local guidelines or a local QS.

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    Written by Koste Team · Koste Chartered Quantity Surveyors · AIQS Member · RICS Member · TPB Registered · 1300 669 400 · info@koste.ai