Provisional Sums: Six Beliefs That Distort a Construction Budget

A provisional sum is an allowance for work that is not yet defined. Treated as a budget line it works. Treated as a fixed price it quietly breaks both cost and programme.

A provisional sum is a figure included in the contract for work that cannot be properly described or measured at tender. It is an allowance to be expended and adjusted, not a price. The confusion between allowance and price is the source of most provisional sum arguments, and it is usually introduced before anyone signs anything.

How to test a claim like this

Take any provisional sum in your contract and ask four questions. Is the work described well enough for the contractor to have programmed for it? Is there an indicative quantity? Does the contract say how it will be instructed and valued? And is the figure a serious estimate or a round number somebody chose to fill a gap? A provisional sum that fails these questions will be expended at a figure unrelated to the allowance, and it will arrive with a programme effect nobody planned for.

Myth 1: A provisional sum is part of the fixed price.

Reality: It is an allowance that is omitted and replaced by the value of the work actually instructed and executed. The contract sum changes accordingly, upward or downward. Treating the allowance as a cap on what the work will cost is the single most common cause of a budget overrun that nobody can explain.

How to check it yourself: Separate provisional sums from measured work in your cost report, and show each one as allowance, instructed value and forecast outturn.

Myth 2: A provisional sum and a contingency are the same thing.

Reality: A provisional sum is an allowance for identified work that is not yet defined, and it sits inside the contract sum where the contractor can see it. A contingency is your own reserve against risk, held outside the contract and released by you. Showing a contingency to a contractor as a provisional sum invites it to be spent.

How to check it yourself: Keep the contingency in the owner budget, never in the pricing document, and record who has authority to release it.

Myth 3: The contractor has programmed for the provisional sum work.

Reality: Whether it has depends on how the sum was defined. Where the work is described with enough information for the contractor to plan it, most conventions treat the contractor as having allowed for it in its programme and preliminaries. Where it is not, the contractor has allowed nothing, and instructing the work brings both cost and a time entitlement.

How to check it yourself: For each provisional sum, state in the preliminaries whether the contractor is required to programme for it, and describe it well enough to make that possible.

Myth 4: A provisional sum can be left as a round number without consequence.

Reality: A figure that bears no relation to the likely cost distorts everything built on the contract sum: the cash flow forecast, the bond amount, the insurance value, the funder facility and your own reporting. It also tells bidders that the documents were rushed, which affects how they price the rest.

How to check it yourself: Base every provisional sum on a real estimate, record the basis, and review the figure before tender rather than after.

Myth 5: Instructing provisional sum work is the same as instructing a variation.

Reality: The expenditure of a provisional sum is usually a defined mechanism in its own right, with its own valuation rules, and in some forms it is treated as a variation while in others it is not. The practical difference shows up in how the work is valued and whether a time entitlement arises, so the clause has to be read rather than assumed.

How to check it yourself: Read the provisional sum clause alongside the variation clause, and record which mechanism will be used before the first instruction.

Myth 6: Unspent provisional sums are a saving you can rely on.

Reality: They are only a saving if the work genuinely is not needed, and much provisional sum work is deferred rather than cancelled. Counting an unspent allowance as a saving in month six, then having to instruct the work in month twelve, produces a reported overrun that is really a forecasting error.

How to check it yourself: Forecast each provisional sum to an expected outturn in every cost report, and release it as a saving only when the work is formally omitted.

Myth 7: Provisional sums only matter to the cost report.

Reality: Undefined work that arrives late affects procurement, sequence and the critical path, and it can also carry its own approval requirements from an authority. The commercial effect is often smaller than the programme effect, and the programme effect is the one nobody budgets for.

How to check it yourself: Put a planned instruction date against every provisional sum in the programme, and treat a missed date as a programme risk rather than a commercial one.

What this changes in your decision

• Define every provisional sum with a description, an indicative quantity and a statement on programming.
• Keep contingency out of the pricing document and under your own control.
• Report each provisional sum separately as allowance, instructed and forecast.
• Fix a planned instruction date for each sum and track it in the programme.
• Read the provisional sum and variation clauses together before the first instruction, and ask your adviser how your form treats the expenditure.

Domira builds and supervises projects across Saudi Arabia, and the commercial discipline above is how its projects stay inside their budget and their programme. Send the drawings, the contract or the site and Domira will tell you where the risk actually sits.