Quantum
Prolongation: time-related cost proved
Prolongation is the actual additional cost of being on site during a compensable period. It is not the tender rate multiplied by the days in an extension, however common that calculation is.
- Jurisdiction
- General; the entitlement mechanism is contract specific
- Law and editions as at
- 3 August 2026
- Last reviewed
- 3 August 2026
- Editorial status
- Editorial draft, not yet independently reviewed
The right period
The compensable period is generally the period during which the delaying event was operating, not the period at the end of the job when the contractor happened still to be there. Costs at the end of a project are frequently different in character from costs during the period of the event, and taking the wrong period is one of the most common quantum errors.
The heads
- Site staff and supervision actually engaged during the period.
- Accommodation, welfare, temporary works and facilities.
- Plant standing or retained, distinguishing standing from working.
- Insurances, bonds and guarantees where the cost is genuinely time-related.
- Subcontractor time-related cost, where it is passed through and evidenced.
Extended duration is not inefficient working
Prolongation compensates for being there longer. Disruption compensates for working less efficiently while there. The two frequently arise from the same event and are proved from different data, and a claim that blends them invites the argument that some cost has been recovered twice.
What has to be reconciled
The claimed cost has to tie back to the accounting records: payroll, ledger, plant returns, invoices and applications. Where preliminaries were priced as a lump sum, the reconciliation between the priced allowance, the actual cost and the claimed amount has to be shown rather than asserted.
Where it fails
- A day rate applied to an extension, with no actual cost behind it.
- The wrong period, usually the end of the job rather than the period of the event.
- Costs that would have been incurred anyway, claimed as if the event caused them.
- Head office overhead smuggled into site cost without a separate basis.
Where the record comes in
Every mechanism on this page turns on evidence: what happened, what was known and when. A record built as the job happens is worth more than any argument assembled afterwards. Construction Metric keeps that record automatically, from the messages, photographs and voice notes a site team already sends.
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Do not overread this page
Whether prolongation cost is recoverable at all, and on what basis, is decided by the contract and the governing law. This page describes how it is proved, not whether it is due.
General explanation of how contract mechanisms, analysis methods and legal principles generally work. It is not legal or contractual advice, not an opinion on any project, and no standard-form contract wording is reproduced anywhere on this site. Standard forms are routinely amended, so every default described here, including every time period, can be different on your project. Your executed contract, as amended, and the governing law and forum always control. Deadlines may already be running: if an event has occurred, preserve your position and take qualified advice.