How to value a construction variation

Published 15 June 2026 · VariationFlow

How construction variations are valued under JCT and NEC contracts, contract rates, fair rates, daywork and forecast cost, plus the records you need to get paid the right amount.

Valuing a variation means putting a fair, defensible price on instructed change. The method depends on the contract, but the principle is consistent: start from the contract, value like-for-like where you can, and keep the records that justify your number.

Start with the contract

Every standard form sets out how variations are valued. Always work from your contract’s valuation rules first, agreeing the method up front avoids most disputes later.

JCT: the valuation hierarchy

Under JCT, variations are typically valued using a hierarchy:

• Contract rates: where the varied work is the same character and conditions as priced work, use the rates and prices in the contract documents
• Pro-rata rates: where work is similar but not identical, adjust the contract rates fairly
• Fair rates and prices: where there is no comparable work, build a fair rate
• Daywork: where work cannot sensibly be measured, value it on the time, materials and plant actually used, plus the contract percentages

JCT also allows for the knock-on effects, for example, where a variation changes the conditions under which other, unchanged work has to be carried out.

NEC: assessed on forecast cost

NEC takes a different route. Compensation events (NEC's version of variations) are assessed on the effect on Defined Cost plus Fee, broadly, the actual or forecast cost of the work plus the contractor's fee. Where the work is still to be done, the contractor submits a quotation based on a forecast; where it is already done, it is based on cost incurred. NEC deliberately avoids fixed pre-agreed rates.

Do not forget time and disruption

A variation's value is not just the direct work. Instructed change can extend the programme or disrupt other activities, and those effects carry cost. Under NEC the time and money are assessed together in the compensation event; under JCT, time (extension of time) and money (loss and expense) may run on separate tracks. Either way, value the whole impact.

The records that protect your valuation

Whatever the method, a valuation is only as strong as its evidence. To get paid the right amount, capture at the time:

• The written instruction (or your confirmation of a verbal one)
• Labour, plant and materials actually used
• Dated photos and site locations
• The programme impact and any disruption to other work

Pricing a variation weeks later from memory is how money gets left on the table.