Price adjustment in Chilean construction contracts: how it works and what to check before signing
Price adjustment — reajuste — is the contractual mechanism that updates the amounts of a construction contract according to the price movement that occurs during execution. Its purpose is to share inflation risk between the parties instead of leaving all of it with the contractor. In Chile its treatment is mainly contractual: the mechanism, the indices and the frequency are defined by the contract.
That means the adjustment clause is one of the ones that moves the most money and one of the least negotiated. On a twenty-month contract with material inflation, the difference between a well-built clause and a poor one can be the entire margin.
The usual mechanisms
Single-index adjustment. The amount is updated by the movement of a single index, typically consumer prices or some construction cost index. It is the simplest to calculate and the least precise: a consumer price index measures a basket of consumption that looks nothing like a project’s cost structure.
Adjustment polynomial. The amount is broken into components — labour, main materials, fuel, plant, a fixed factor — and each component is updated with its own index. It is more precise and more laborious.
No adjustment. The contract is at firm prices. It is common on short projects and shifts all inflation risk to the contractor. On long projects it is a bet.
| Mechanism | Precision | Complexity | When it suits |
|---|---|---|---|
| Single index | Low | Low | Short projects, stable inputs |
| Polynomial | High | High | Long projects, volatile inputs |
| No adjustment | — | None | Only on very short durations |
How a polynomial works
The logic is simple even if the formula is intimidating. You define what share of the cost each component represents, and each one is updated with the index that best represents it.
An example structure:
| Component | Share | Index |
|---|---|---|
| Labour | 30 % | Sector wage index |
| Steel | 15 % | Steel price index |
| Cement and concrete | 20 % | Materials index |
| Fuel and energy | 8 % | Fuel index |
| Other materials | 17 % | General materials index |
| Fixed component | 10 % | Not adjusted |
The fixed component matters and is usually negotiated: it represents the part of the cost that does not move with inflation, and the higher it is, the less adjustment the contractor receives. A polynomial with a 30 % fixed component protects considerably less than one with 5 %.
The principle that makes a polynomial fair: the shares must reflect the real cost structure of that project. A generic polynomial that assigns 15 % to steel does not protect what it should on a steel-intensive project.
What to check in the clause, before signing
Seven concrete points. Each one can cost money.
Baseline date. From when is the movement measured? Bid date, signing date, start date? There can be months between them, and inflation already happened in those months.
Specific indices. Which ones exactly, published by whom? “Construction index” with nothing further is a guaranteed source of argument.
Frequency. Monthly, quarterly, by milestone? The more spaced out, the more the contractor is financing.
Calculation base. Is the period’s progress adjusted, the pending balance, or the total? Those are very different results.
Fixed component. What percentage is not adjusted?
Cap or trigger. Is there a minimum movement for it to activate? Is there a maximum cap? A cap in a high-inflation period can leave out exactly what you needed covered.
Treatment of delays. If the project falls behind for its own reasons, is the additional period adjusted? Usually not, and it is worth knowing. If the delay is not attributable to you, is it expressly covered?
That last point is the one most often forgotten and the most argued about at the end. If your contract does not distinguish between your own delay and someone else’s for adjustment purposes, you are going to argue about it.
The most common calculation errors
Wrong baseline date. Using the signing date when the contract says bid date, or the other way round.
Outdated or discontinued index. Agencies change methodologies and sometimes discontinue series. If the clause references an index that stopped being published, you have to resolve what replaces it, and it is best if the contract anticipates that case.
Adjusting over already adjusted amounts. A carry-forward error in monthly spreadsheets that accumulates silently.
Applying adjustment to the unamortised advance. The advance was received at the value of a given date; adjusting it is charging twice.
Not adjusting extra work. Extraordinary prices agreed at a later moment have their own baseline date. Treating them with the original contract’s date distorts the calculation in both directions.
Filing the adjustment without workings. Same as with quantity take-offs: a number without the derivation is an assertion, and the inspection will query it.
What to do during the project
Adjustment is not just arithmetic at month end. Three practices.
Keep the published indices for each period. It sounds trivial until an index is retroactively corrected or changes methodology mid-project.
Keep the workings month by month, do not reconstruct them. An eighteen-month cumulative adjustment rebuilt at the end is error-prone and hard to audit.
Record relevant economic events in the libro de obras. A sharp rise in an input, a supply shortage, a forced change of supplier. It strengthens any later conversation about the mechanism.
Frequently asked questions
- Does the adjustment apply to retentions?
- It depends on the contract. Retention is usually calculated on the already adjusted amount, but it is worth verifying, because some contracts treat it the other way round.
- Can I negotiate the polynomial before signing?
- On private contracts, almost always, and it is worth trying. Bring your real cost structure to the conversation: it is a technical argument, not a request. In public tenders the mechanism usually comes fixed in the bidding documents.
- What if the adjustment comes out negative?
- If the indices fall, the mechanism can produce a downward adjustment. Well-drafted contracts contemplate it expressly in both directions.
- Is a contract without adjustment a good idea on a short schedule?
- Over a few months it can be reasonable and it simplifies administration. The question is what happens if the project runs long. A clause that switches the adjustment on beyond a certain duration is a reasonable middle ground.
- How do I estimate the impact of adjustment when budgeting?
- Project the expected inflation of your main inputs over the project duration and compare it with what the mechanism will give back. The difference is risk you are taking on, and it belongs in your appraisal of the project rather than arriving as a surprise.
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