NEC Clause 51: Certifying Payment

NEC clause 51 turns the assessed amount due into a certificate and a payment. Under the NEC4 and NEC3 Engineering and Construction Contracts, the Project Manager certifies within one week of each assessment date, and payment is made within three weeks of that date unless the Contract Data gives a different period.

The clause also covers what happens when things run late, and payments going the other way. It follows clause 50, which works out the amount. Both are explained in our NEC payment and Defined Cost guide.

What each part does

Clause	Rule	Worth noting
51.1	A certificate is due from the Project Manager a week or less after each assessment date	The opening payment equals the amount due. Later ones are the change since the previous assessment
51.2	Payment by three weeks after the assessment date, or in the Contract Data period. Late payment carries interest	Interest also applies if the payment is late because no certificate was issued
51.3	A correction in a later certificate carries interest in stated cases	From when the wrong amount was certified until the changed amount is certified
51.4	Interest is daily at the Contract Data rate, and compounded annually	Same in both editions
51.5 in the NEC4 ECS	Tax the law requires one Party to pay the other is added to a payment	NEC3 ECC puts tax into the amount due at 50.2. Check the position in your NEC4 ECC

NEC4 also expects the certificate to show how the amount has been assessed. In NEC3 the same duty sits at 50.4.

Worked example: a payment back to the Client

Illustrative figures on a fictional Option C job, in which assessments fall every four weeks.

Assessment	Amount due	Certified payment	Direction
1	£200,000	£200,000	Client to Contractor
2	£350,000	£150,000	Client to Contractor
3	£330,000	£20,000	Contractor to Client
4	£460,000	£130,000	Client to Contractor

At assessment 3, a forecast from assessment 2 was too high and some cost was disallowed, so the amount due fell. The contract says the Contractor pays that difference. In a real account, parties often deal with this by carrying a small negative into the next cycle. If that's agreed, record it.

When the certificate is late

Clause 51 doesn't stop the clock for the Contractor. A late or missing certificate doesn't remove the right to be paid, and it brings interest with it. Under Option Y(UK)2 the certificate is also the payment notice, so it matters for the statutory process too. The payment timeline shows how the dates fit together, and if the Contractor is still waiting, the Construction Act provides a route for the payee to give its own notice. Take advice before relying on that.

Interest in practice

The Contract Data states the interest rate. A short example with illustrative figures: £100,000 paid 14 days late at 5% a year is about £192 (£100,000 × 5% × 14 ÷ 365). It goes into the next assessment once the late payment has been made, so it appears as another line under clause 50. Small amounts of this kind get forgotten, and tracking them is easier when your register holds both the due date and actual payment date.

Corrections and when interest follows

Under 51.3, interest on a correcting amount covers three broad cases: the Project Manager corrects a mistake or a compensation event, an Adjudicator or tribunal changes the amount, and, in the NEC4 subcontract, a test or inspection was needlessly delayed and that held up a payment. So a compensation event that should have been assessed earlier and is corrected later can carry interest, which is a reason to keep assessments moving.

What people get wrong

• Measuring three weeks from the certificate. It runs from the assessment date.
• Forgetting the Contract Data entry. Many clients state a longer or shorter period. Option Y(UK)2 then has its own due date and final date, covered under pay less notices.
• Treating a certificate as final. Each interim certificate can be corrected, and payment doesn't mean the work's value is settled.
• Assuming the subcontract matches. The NEC4 and NEC3 subcontracts allow two weeks to certify and four weeks to pay. See payment for NEC subcontractors.

Related guides

• NEC Payment and Defined Cost: The Complete Guide
• NEC Clause 52: Defined Cost Accounting
• The NEC Payment Timeline
• Assessment Date and Assessment Interval
• Price for Work Done to Date (PWDD)
• NEC Clause 50: Assessing the Amount Due

This guide is general information in our own words, not legal advice. Your contract and its Contract Data always govern. NEC, NEC3 and NEC4 are trade marks of Thomas Telford Ltd; Contract Status is not affiliated with or endorsed by NEC.