What Is a Provisional Sum in Construction? A Commercial Contractor’s Guide

By

Josh Krissansen

Last Updated Aug 31, 2026

By

Josh Krissansen

On certain commercial projects, some work packages cannot be fully scoped or priced at tender. Design may be incomplete, ground conditions may be unconfirmed, and authority information may still be outstanding, preventing the project from being fully scoped at tender.

Provisional sums exist to handle that uncertainty within the contract, holding an estimated allowance in place until the actual cost of the work can be confirmed and substituted.

In this guide, we cover how provisional sums work, how the superintendent assesses and adjusts provisional sum claims, and how to track and close out provisional sum items so that you can manage exposure without it becoming a source of disputes or delayed final account settlement.

What is a provisional sum in construction?

A provisional sum is an estimated allowance for a specific item of work included in the contract sum where the scope cannot be fully defined at tender. Unlike a lump sum item, the allowance is not usually treated as a fixed price. It is a placeholder that is omitted and replaced with the amount assessed under the contract once the work is directed, scoped and costed.

Common provisional sum items on commercial projects include:

• Bulk earthworks where ground conditions are unknown
• Rock removal
• Deep drainage where invert levels are not yet confirmed
• Specialist subcontractor packages where the design is incomplete at tender

A provisional sum is not the same as a contingency.

A contingency is usually a separate project reserve held outside the specific provisional sum mechanism. A provisional sum is a defined contract item with its own description, allowance figure and adjustment process.

How provisional sums work under Australian contracts

Provisional sums aren't just budget estimates—they are strict contractual rules. Under standard Australian contracts (like AS 4000 clause 3 and AS 2124 clause 11), the process follows three main steps:

1. 1. The Trigger: The head contractor carries out the work once directed by the superintendent.
2. 2. The Swap: The original allowance is removed from the total contract price and replaced with the actual, reasonable cost of the work.
3. 3. The Margin: The contractor adds their agreed overhead and profit margin on top of that final cost.

The superintendent's role

The superintendent reviews the contractor’s evidence—such as invoices and timesheets—to confirm the claimed costs are fair. Under standard contracts, this adjustment isn't treated as a variation and doesn't require prior approval from the client.

You can claim these adjustments in your regular monthly progress payments under Security of Payment laws, provided you list them separately from variations and attach proof of cost.

Provisional sum vs prime cost item

Contracts administrators regularly encounter both provisional sums and prime cost items in contract schedules. Knowing the difference matters because the adjustment mechanism and supporting evidence requirements differ for each.

A provisional sum covers both labour and materials for work whose scope is not yet defined. A prime cost item covers the supply cost of a specific material or fixture that has not yet been selected.

For instance, a provisional sum might exist for rock excavation where the volume and class cannot be confirmed until bulk earthworks begin, whereas a prime cost item might be used for a tapware package or stone benchtop selection is deferred where the principal has not finalised finishes at tender.

The adjustment mechanism also differs. Provisional sum adjustments replace the allowance with the full actual cost of the work. Prime cost adjustments replace the supply-only allowance with the actual supply cost, with the installation component remaining in the lump sum.

Contracts administrators should ensure the contract schedule correctly categorises each item, as misclassification affects how overhead and profit are calculated, and what supporting evidence the superintendent will require. A provisional sum misclassified as a prime cost item, for instance, leaves the labour component outside the adjustment mechanism entirely, which means the head contractor cannot recover those costs through the standard process.

How provisional sum adjustments are assessed and claimed

When provisional sum work is completed, or its scope is confirmed, the head contractor submits a provisional sum adjustment claim to the superintendent with supporting evidence of actual cost. Depending on the nature of the work, that evidence will be:

• Subcontractor invoices
• Time and materials records
• An agreed schedule of rates

The superintendent assesses the claim against the contract's definition of reasonable cost and the overhead and profit rates stated in the contract. If the actual cost exceeds the allowance, the contract sum increases by the difference plus the margin. If it falls short, the principal receives a credit.

Submit provisional sum adjustments as soon as actual costs are confirmed, with complete supporting documentation. Claims submitted late or bundled with unrelated progress claims are harder to assess and more likely to be disputed. Claims submitted outside the contractual time bars may be rejected by the superintendent regardless of their merit.

Overhead and profit on provisional sum adjustments

Under standard-form AS 4000 and AS 2124, the head contractor is generally entitled to recover overhead and profit on the cost of provisional sum work, though the applicable rates and the base to which they apply will depend on what is stated in the contract schedules.

• Applying the margin to the right base

  The most common error that occurs here is applying the margin to the wrong base. Overhead and profit apply to the actual cost of the work, not to the difference between the actual cost and the provisional sum allowance.

• Reasonable overhead and profit entitlements

  Where the contract doesn't specifically mention rates, the head contractor is generally entitled to reasonable overhead and profit, though what constitutes reasonable will be assessed by the superintendent and is often lower than what the contractor expects. Fixing rates in the contract at tender eliminates that dispute entirely.

• Subcontracted provisional sum work

  On subcontracted provisional sum work, the head contractor's margin applies to the subcontractor's invoice. Confirm whether the contract permits a second layer of margin where the subcontractor has also included overhead and profit in their price.

Setting a provisional sum allowance at tender

Setting a realistic provisional sum allowance starts with the information available at tender.

Site investigation data, geotechnical reports, and authority pre-engagement outcomes form the primary reference points, and while Rawlinsons unit rates provide a useful benchmark, they need to be adjusted for site-specific conditions and current market pricing.

Document the basis for each provisional sum allowance in the tender submission or contract schedules. A clear statement of assumptions reduces scope for the superintendent to dispute what work the provisional sum covers.

Where the allowance is based on limited information, note the specific assumptions and flag the risk to the principal before contract execution. Gaps surfaced at tender are far easier to manage than gaps surfaced mid-delivery.

Tracking provisional sum exposure through cost reports and cash flow

Each provisional item carries an allowance that will be omitted and replaced with actual cost, and until that substitution is confirmed, the gap between the two is essentially a financial risk, making a structured approach to tracking vital.

The best practice here is to track provisional sums as a separate line item category in the project cost report, distinct from variations and contingency. Mixing provisional sum items with variations obscures the financial position and makes accurate reporting to the principal impossible.

For each provisional sum item, record the original allowance, forecast actual cost, committed cost to date, and remaining exposure. Then, be sure to update this register at every cost report cycle so the project manager has a live view of where provisional sum items are tracking against budget.

Cash flow forecasting needs to reflect provisional sum timing as well. The drawdown forecast should show when actual costs will be confirmed and claimed, not when the allowance was originally scheduled. Where those dates have shifted, the forecast needs to move with them.

Where a project carries multiple provisional sum items, maintain a standalone register separate from the variation register. This matters at final account, where a clean audit trail for each item reduces the risk of amounts being missed, duplicated, or disputed during close-out.

Closing out provisional sums at final account

Begin provisional sum close-out before practical completion, not after. By the time practical completion is reached, open provisional sum items without confirmed costs create delays to final account and give the superintendent grounds to dispute amounts that should have been resolved during delivery.

For each item, omit the original allowance, substitute the actual cost, and calculate the overhead and profit adjustment in line with the contract rates. Then, make sure you obtain the superintendent's written agreement to the adjusted amount before final account is lodged.

Compile full supporting documentation for each item: subcontractor invoices or time and materials records, the superintendent's written direction to carry out the work, and the overhead and profit calculation.

Where a provisional sum item was never called up by the superintendent, omit the full allowance from the contract sum. Where work was not directed, the head contractor will generally have no basis to claim the provisional sum allowance.

Provisional sums are a standard tool for managing contract uncertainty on commercial projects

Understanding how provisional sums work under standard contracts gives head contractors and contracts administrators the foundation to assess claims correctly, apply overhead and profit to the right base, and close out items without disputes at final account.

The financial exposure they represent is manageable when allowances are set with care at tender, tracked through delivery, and documented thoroughly before practical completion.

Written by

Josh Krissansen

122 articles

Josh Krissansen is a freelance writer with two years of experience contributing to Procore's educational library. He specialises in transforming complex construction concepts into clear, actionable insights for professionals in the industry.

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