Installment payments can balance cash flow and performance risk, but only when each amount is tied to a clear stage and a way to verify completion. A contract that says “pay as work progresses” without defining progress can lead to disputes over when money is due and whether the work is acceptable.

Define each milestone

Break the work into observable stages: mobilisation, design approval, completion of a production batch, delivery of specified goods, installation, testing or final acceptance. For each milestone, state the responsible party, deliverable, deadline, quality standard and any dependencies. Avoid milestones described only as a percentage of progress unless the parties also define how that percentage will be measured.

Specify the evidence required for payment

Identify the documents that support an invoice, such as an approved progress certificate, inspection report, delivery note, test result, timesheet or signed acceptance. State who reviews the evidence, the review period and how objections must be made. Explain whether silence counts as acceptance and consider whether that rule is appropriate for the transaction.

Coordinate payment with acceptance and defects

Distinguish delivery from acceptance. If the buyer finds a defect, provide a process to record it, require correction and verify the correction. Decide whether the undisputed part of a payment remains payable while a limited issue is resolved. For long projects, consider retaining a stated portion until final completion or the end of a defined warranty period, where commercially appropriate.

Handle delay, change and cancellation

Set out what happens if a milestone is late, incomplete or changed. Include written change approval, any price or schedule adjustment, notice of delay and the consequences of suspension or termination. Align advance recovery, refunds and final account calculations with the work actually completed and materials delivered.

Practical checklist

• Does every installment have a date or objective trigger?
• Can the required evidence be produced and checked?
• Are review, objection and correction periods clear?
• Do invoices and payment dates match the project schedule?
• Are taxes, currency, bank details and supporting records addressed?

Keep signed approvals, evidence, invoices and transfer receipts in one project file. This article is general information, not legal advice; tailor payment terms to the contract, project and applicable law.