Fixed-Price Construction Contracts and Inflation Risk: Are You Covered?

Producer input prices rose 7.7% in April (Office for National Statistics, 2026). If you are a contractor working under a fixed-price deal, that number should make you uncomfortable.

The direction of travel is clear. Geopolitical tension, including conflict involving Iran, has pushed oil and energy prices higher. Steel, concrete, diesel, and labour costs are moving in the same direction. The contract price you agreed six months ago was based on a different world.

Most contractors know this. What they don’t always know is whether their contract protects them, and what happens if it doesn’t.

At Helix Law, we work with contractors, subcontractors, and employers across construction disputes. We find it striking how often inflation risk is never properly addressed at the tendering stage. By the time the cost pain becomes acute, the options have narrowed considerably.

What Does a Fixed-Price Contract Actually Mean for Inflation Risk?

If you have signed a fixed-price contract with no fluctuation mechanism, general price inflation is your risk. Full stop.

There is no freestanding legal right to more money because your materials now cost more than you expected. You cannot claim the contract has become impossible. You cannot invoke force majeure simply because your margin has been eroded. Attempts to argue that rising costs amount to frustration of the contract almost always fail. The doctrine requires performance to become radically different in nature, not merely more expensive.

Contract law is unforgiving in this respect. The paying party is entitled to insist on the agreed price, however uncomfortable that position may be for the contractor.

The only exception is where the contract itself creates a mechanism for price adjustment. That is where the JCT fluctuation provisions and NEC secondary Option X1 come in.

JCT Fluctuation Options, What Is in Your Contract?

The JCT suite of contracts offers three approaches to inflation risk (Blundell & Sekkar, 2022). Understanding which one applies to your project, or whether any applies at all, is the first thing to check.

Option A: Contributions, Levies and Taxes

Option A covers changes in statutory contributions, levies, and taxes: National Insurance contributions, for example, or the Construction Industry Training Board levy. It does not address material cost increases. If steel, concrete, or diesel spikes, Option A will not help you.

Option B: Labour and Materials Fluctuations

Option B goes considerably further. It adjusts the contract sum to account for increases, or decreases, in the cost of labour and materials from the Base Date. Fuel and electricity are also included. If market prices move after the Base Date, the adjustment mechanism shares that risk between the parties rather than leaving it entirely with the contractor.

Option C: Full Fluctuations Formula

Option C is the most comprehensive. Rather than tracking specific categories of cost, it uses published price indices to calculate a composite adjustment factor applied during the project. It is designed for longer, more complex contracts where tracking individual material costs is impractical.

The critical point is this. In benign markets, when input price movements are modest and predictable, employers and main contractors routinely cross out Options B and C in the Contract Particulars. Sometimes this happens as a matter of commercial bargaining power. Sometimes it happens on autopilot. The effect is to convert the contract into a de facto fixed price.

Check what options have been selected before you bid. Not after you start.

If you are currently on a live project and Options B or C were struck out, that decision has consequences, but there may still be avenues worth exploring, including whether notice requirements were properly observed and whether other mechanisms in the contract might assist.

NEC Contracts and Option X1

Under NEC contracts, the position is different in form but similar in effect. General inflation is not a compensation event under the core NEC clauses. Unless you can point to a qualifying event, a specific employer instruction, a change in law, a prevention event, you are not entitled to more money simply because your input costs have risen.

The mechanism for addressing inflation under NEC is secondary Option X1: Price Adjustment for Inflation (Patterson, 2022). When X1 is selected, the parties agree a base date, set out the relevant indices and proportions in the Contract Data, and an index-based factor is then applied to each payment assessment during the project. Done properly, it provides a transparent and auditable mechanism for sharing inflation risk.

But X1 has to be switched on. If it is not in your contract, inflation sits with you.

There is a further practical point. Even where X1 is selected, the mechanism only works if your records and assessments are accurate. Getting the inputs right — the baseline cost breakdown, the correct index references, the timing of assessments — matters. Poorly maintained records will undermine a legitimate entitlement, even one that clearly exists on paper.

Subcontract Alignment

Whether you are working under JCT or NEC, a problem that frequently arises is a mismatch between the main contract and the subcontracts below it. A main contractor may have Options B or C, or NEC X1, in the main contract, but may have let subcontracts on a lump sum with no equivalent mechanism. That mismatch creates exposure at the subcontract level, and it is often overlooked at the procurement stage.

If your subcontract position does not mirror your main contract position, you have a gap. Identifying it early, and addressing it through contractual notices or commercial negotiation, is substantially easier than trying to unwind it once the project is in deficit.

A Price-Risk Checklist for Contractors

Whether you are reviewing a contract before signing or trying to understand your position on a live project, the following are the questions that matter:

• Which JCT fluctuation option has been selected — A, B, or C — or have Options B and C been struck out in the Contract Particulars?
• Is NEC secondary Option X1 selected, and if so, what indices and proportions are agreed in the Contract Data?
• What is the Base Date, and how far has the project deviated from the original programme?
• Do your subcontracts mirror your main contract position on inflation risk?
• Have any relevant notices been served, and if not, is there still time?
• On live projects, have you audited your entitlements under the existing mechanisms, even if the position looks unfavourable?

The last two points deserve emphasis. Construction contracts are heavily notice-dependent. If there is a fluctuation mechanism in your contract, your ability to recover under it may be conditional on timely notices. Waiting until the cost pain becomes terminal before engaging with the contractual machinery is one of the most common, and most avoidable, mistakes we see.

Inflation Risk in Construction Contracts Is Not Going Away

Producer input prices are up 7.7% in April. Geopolitical tension continues to push energy and materials in one direction. The 2021–2022 experience, when contractors locked into fixed-price deals watched their margins erode in real time, is not ancient history.

The question is not whether inflation risk is present on your project. The question is whether your contract allocates it to you, whether there is a mechanism to recover it, and whether you have done what the contract requires to preserve that entitlement.

We will tell you plainly what your contract gives you and what it doesn’t. At Helix, we are specialists in construction disputes, and we back our advice, offering Conditional Fee Agreements (no win no fee) for qualifying construction claims where the value exceeds £10,000 and the prospects of success are strong.

If you want to understand your position, get in touch with our team for a no-cost, no-obligation initial conversation.

Frequently Asked Questions

Can I Claim for Inflation if I Have a Fixed-Price Contract With No Fluctuation Clause?

In general, no. Unless you can point to a specific entitlement in the contract, a fluctuation provision, a compensation event, a change instruction, you are bound by the agreed price. Inflation alone does not entitle you to more money. That is true even if the cost increase is significant and was genuinely unforeseeable when you entered the contract.

What Is a Base Date in a Construction Contract, and Why Does It Matter?

The Base Date is the reference point from which price adjustments under JCT Options B and C, or NEC Option X1, are calculated. If the Base Date predates your actual start on site by a significant margin, or if the project has been extended, the gap between the Base Date and the current position determines the scale of potential recovery. Getting the Base Date right, and understanding what it means in the context of your project’s programme, is a practical priority.

What if My Project Has Been Delayed or the Programme Extended Significantly?

Programme extension makes the inflation problem considerably worse. The longer the project runs beyond the original programme, the longer your cost base is exposed to market movements, without a corresponding adjustment in the contract price if no fluctuation mechanism applies. Where delays have been caused by employer acts or instructions, there may be separate arguments about time and money. These are worth examining carefully, not least because the value in dispute can be substantial.

When Should I Involve a Construction Solicitor in an Inflation or Cost Dispute?

Before you need one, ideally. The best time to identify whether your contract protects you against inflation risk is at the tendering stage. The second best time is the moment you sign. If you are already on site and your costs are rising, engage now rather than later, particularly if there are notice obligations that need to be served or records that need to be put in order. The window for protecting your position can close quickly, and it is much easier to build an entitlement prospectively than to reconstruct one after the event.

References

Blundell, N., & Sekkar, H. (2022, October 14). Three options for managing inflation risk using JCT construction contracts. The Joint Contracts Tribunal. https://corporate.jctltd.co.uk/three-options-for-managing-inflation-risk-using-jct-construction-contracts/

Office for National Statistics. (2026, May 20). Producer price inflation, UK: April 2026. https://www.ons.gov.uk/economy/inflationandpriceindices/bulletins/producerpriceinflation/april2026

Patterson, R. (2022, May 23). How to use NEC secondary option X1 on price adjustment for inflation. NEC Contracts. https://www.neccontract.com/news/how-to-use-nec-secondary-option-x1-on-price-adjustment-for-inflation