What is practical completion? What the certificate means, what changes on the day, and why your completion and the project’s are different dates

Published 29 September 2026 · VariationFlow

A plain-English guide to practical completion for UK subcontractors: what it means and the test the courts apply, who certifies it under JCT and NEC, what changes on the day (retention, the rectification period, delay damages, the final account clocks), sectional completion and partial possession, and why a sub-contract that keys your dates to the main contract’s completion is worth reading twice.

Your package finished in March. The project handed over in December. The sub-contract released half your retention at practical completion, and the question nobody asked at tender was whose. If the answer is the project’s, your money sat with the contractor for nine months longer than it needed to, and the second half is a year further away again. Practical completion is the date most of the money on a job is counted from, and it is a date with more than one meaning.

What it means

Practical completion is the point at which the works are complete for the purposes of the contract, marked by a certificate or a written statement from the person the contract appoints to decide it: the Architect or Contract Administrator under the JCT Standard Building Contract, the Employer under the Design and Build form, the contractor under the JCT sub-contracts, and under NEC, where the concept is called Completion, the Project Manager on the main contract and the Contractor on the subcontract. The contracts deliberately do not define the word, and the courts have declined to give it a formula.

The general position, restated by the Court of Appeal in Mears v Costplan in 2019, is that practical completion is a matter of degree. Outstanding items that are trifling do not prevent it, whether they are defects or incomplete work, and the question is the nature and extent of what is outstanding, not the cost of putting it right. A non-trivial defect can prevent practical completion however cheap it is to fix. So a snagging list does not, by itself, stop the certificate; a snagging list with something serious on it does.

What changes on the day

• Retention. Under most forms half the retention is released at practical completion, taking the hold to half the percentage, and the balance is released at the end of the rectification period once defects are made good. On a five percent retention that is the day the first two and a half percent falls due.
• The rectification period starts. The defects liability or rectification period, commonly twelve months, runs from practical completion, and it ends with the certificate or statement of making good defects that releases the rest of the retention.
• Delay damages stop. Liquidated damages for late completion run to practical completion and no further, so the certificate fixes the number of weeks any delay claim is measured over.
• The final account clocks start. Under the JCT main contract forms the contractor sends the documents needed to adjust the contract sum within six months of practical completion and the quantity surveyor’s statement of adjustments follows; under NEC4 there is no final account as such: on the subcontract the Contractor assesses the final amount due after the Defects Certificate, inside the period clause 53 sets, as the Project Manager does on the main contract. Your sub-contract has its own version of whichever applies.
• The interim cycle continues. Under the JCT 2016 forms the monthly Interim Valuation Dates keep running after practical completion, so every month until the final payment is still a cycle with a due date and a set of notices.

Whose completion

A sub-contract has its own practical completion, of the sub-contract works, and it will usually fall months before the project’s. Where the sub-contract keys your retention release and your rectification period to your own completion, the dates above run from March in the example. Where it keys them to the main contract’s certificate, they run from December, and the money waits.

Since the 2011 amendments to the Construction Act there is a limit on how far that can go. Section 110(1A) says a contract does not provide an adequate payment mechanism where payment is conditional on the performance of obligations under another contract or on a decision by any person as to whether those obligations have been performed. A clause that releases your retention only on the certificate of making good defects under the main contract is caught by it, and where the contractual mechanism fails the Scheme for Construction Contracts fills the gap. Retention that has fallen due is part of the notified sum like everything else. None of that stops the clause being written, and it is written into most sub-contracts; it means the clause is worth challenging rather than accepting.

Sections and partial possession

Where the contract divides the works into sections, each section has its own practical completion, its own rectification period and its own share of the retention and the delay damages, and the certificate for a section triggers the consequences for that section alone. Where the employer takes possession of part of the works before completion, with the contractor’s consent, the JCT forms treat that part as practically complete from the date of possession for the purposes of retention, defects and damages. Both are worth knowing about on a phased job, because they bring some of the money forward.

Getting the date fixed

• Ask for it in writing. On a sub-contract the contractor decides when your works are practically complete, and a contractor with your retention in its account has no reason to hurry. A written request for the statement, with the snagging list attached and the serious items cleared, starts the conversation on a date.
• Keep the snagging list separate from the defects list. Trifling items on a list do not prevent completion; a serious one does. Clear the serious ones first and say which they were.
• Record the certificate date, not the day the work stopped. Every clock above runs from the certificate.
• Diarise the end of the rectification period on the day the certificate arrives, and the retention release date with it. The second half of the retention is the money most often written off, and it is written off because nobody put the date in a diary a year earlier.

How VariationFlow uses the date

The practical completion date is recorded on the project once, and the retention position, the final-account timetable and the payment cycles that continue after completion all read from it, so the retention release and the end of the rectification period appear as dated rows rather than as something to remember. Where a sub-contract keys the release to the main contract instead, the record shows which date it is running from, so the question of whose completion is asked at the start rather than at the end.

This guide is general information rather than legal advice. Whether particular works have reached practical completion, and what your own sub-contract makes turn on it, are questions about the facts and the words of your contract, and both are worth an adviser’s eye before a certificate is refused or accepted.