Commercial & Contract · Mandatory · Construction

Interim Payment Certificate

A certificate issued by the contract administrator confirming the amount due for an interim payment.

Last reviewed: 29 March 2026 — This guide reflects UK law as of this date. JCT / Contract remains current with no amendments enacted as of 29 March 2026. Next scheduled review: 29 March 2027.

Legal basis	JCT Standard Building Contract (SBC) / Intermediate Building Contract (IC) + Housing Grants, Construction and Regeneration Act 1996
Issued by	The contract administrator (CA) — typically the architect or quantity surveyor named in the contract. The CA acts independently, not as the employer's agent for certification purposes.
Timing	Under JCT 2024, the interim certificate must be issued within 5 days of the payment due date. The certificate constitutes the employer's payment notice under s.110A of the Construction Act 1996.
Independence	The CA's independence when certifying is fundamental — the CA must assess the value of work carried out impartially, without instruction from the employer on what amount to certify

1. Interim Certificate — The CA's Independent Payment Assessment

The interim payment certificate is issued by the contract administrator after each interim valuation under JCT standard form contracts. It is the CA's independent assessment of the value of work properly executed by the contractor, including the value of materials on site, variations, daywork, and any other adjustments provided for under the contract. The certificate determines the sum that the employer is obliged to pay and constitutes the employer's payment notice under the Construction Act 1996.

The CA's independence when certifying interim payments is fundamental to the operation of JCT contracts. Although the CA is appointed and paid by the employer, when exercising the certification function the CA must act impartially and must not be influenced by the employer's commercial interests. The CA's duty is to assess the value of the work carried out on the basis of the contract terms, the contractor's application, site inspections, and professional judgement. The certificate must reflect a genuine assessment of the work done — not a figure that the employer would prefer.

Under JCT 2024, the interim certificate must be issued within 5 days of the payment due date. Where the CA fails to issue a certificate within this period, the contractor's payment application may become the notified sum under s.110A of the Construction Act 1996, with the same consequences as a missed payment notice — the full amount applied for must be paid by the final date for payment. The CA's failure to certify on time can therefore have significant and immediate financial consequences for the employer.

The CA must be commercially independent when certifying

The contract administrator's independence is a cornerstone of JCT contracts. When certifying interim payments, the CA must exercise independent professional judgement based on the work carried out, the contract terms, and the evidence available. An employer who instructs the CA to under-certify, delay certification, or withhold certificates is interfering with the CA's independent function — which constitutes a breach of contract by the employer. If the contractor can demonstrate that the CA has failed to act independently, the certificates may be set aside and the employer may face a claim for damages.

2. Interim Payment Certificate — Content

Field	Detail
Certificate number	Unique sequential number for each interim certificate (e.g. IPC-001, IPC-002). Provides a complete audit trail from the first certificate through to the final certificate.
Date	The date on which the certificate is issued by the CA. Must be within 5 days of the payment due date under JCT 2024.
Contract reference	Project name, site address, and contract reference. Identifies the contract to which the certificate relates.
Gross value	The total gross value of all work properly executed from commencement to the date of the valuation. Includes the contract sum work, variations, daywork, fluctuations, and any other items valued under the contract.
Retention	The retention percentage applied to the gross value (typically 3–5% under JCT). The certificate should state the retention rate, the retention amount, and whether any retention has been released (half at practical completion, balance at end of rectification period).
Materials on site	The value of materials and goods delivered to site but not yet incorporated into the works. Must be properly stored, protected, adequately insured, and clearly identifiable as intended for the works. The CA must be satisfied that the materials meet these requirements before including their value in the certificate.
Previous certificates	The total amount previously certified in all preceding interim certificates. Deducted from the current gross value (less retention, plus materials) to calculate the sum due this period.
Net sum certified	The net sum certified as due for this interim period — the gross value less retention, plus materials on site, less the total of all previous certificates. This is the amount the employer must pay by the final date for payment.
Final date for payment	The date by which the employer must make payment of the net sum certified. Under JCT, typically 14 days after the due date (as specified in the contract particulars). Failure to pay by this date entitles the contractor to interest and to exercise the right to suspend.
CA signature	The name, professional qualification, and signature of the contract administrator issuing the certificate. The certificate must be issued by the named CA (or a validly appointed replacement) — a certificate issued by an unauthorised person is not valid.

3. Common Mistakes

CA under-certifying under employer pressure

This is the most serious and most damaging mistake a contract administrator can make. When an employer instructs or pressures the CA to certify less than the true value of the work carried out — whether to manage cash flow, to exert commercial pressure on the contractor, or for any other reason — the CA is failing in the independent certification function that is fundamental to the JCT contract. Under-certification deprives the contractor of money that is properly due and can cause serious cash flow damage throughout the supply chain. The contractor's remedy is to refer the matter to adjudication, where the adjudicator will determine the true value independently. If the CA's lack of independence is established, the employer may also face a claim for breach of contract and the CA may face professional misconduct proceedings.

4. Frequently Asked Questions

What if the employer disagrees with the CA's certificate?▾

The employer cannot override the CA's certificate. Under JCT, the CA's interim certificate is the payment notice, and the sum certified is the notified sum that the employer must pay by the final date for payment. If the employer considers that the CA has over-certified, the employer's remedy is to serve a pay-less notice within the prescribed period before the final date for payment, specifying the sum the employer considers due and the basis for any deductions. If no valid pay-less notice is served in time, the employer must pay the full certified amount. The employer may also raise the matter with the CA for future certificates, but cannot retrospectively alter a certificate that has been issued. If the dispute cannot be resolved, either party can refer it to adjudication under the Construction Act 1996.

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