Construction progress invoice timing in Belgium: control the milestone and the fifteenth-day deadline

A construction progress claim and an invoice are related but not identical records. Before issuing the invoice, the contractor should identify the VAT event, the approved milestone and the period to which the work belongs. Belgian economic guidance notes that VAT rules can require certain businesses to issue an invoice no later than the fifteenth day of the month following delivery. The exact application depends on the transaction, so the operational record must expose the underlying dates.

Separate measurement from approval

Record the measured quantities, contractual percentage or milestone and supporting site evidence. Then record who approved the claim and when. A draft progress statement prepared by the site manager does not automatically establish the invoice date. Variations, retention and disputed quantities should remain visible rather than being rolled into one unexplained total.

Identify the relevant VAT event

Capture the delivery, completion, payment or other event relevant to the transaction and obtain advice where the rule is unclear. Do not simply use the day the office opened the document. The invoice workflow should show the source date, the calculated operational deadline and the person responsible for confirming it.

Control the fifteenth-day calculation

Where the cited VAT deadline applies, calculate the fifteenth day of the following month from the correct event. Use calendar logic rather than adding a fixed number of days. Flag the item early enough for project evidence and customer references to be completed. A warning is useful only when the user can see why that date was chosen.

Prepare the structured invoice

For an in-scope Belgian B2B invoice issued from 1 January 2026, the official e-invoicing FAQ requires a structured electronic invoice. Verify customer identity, Peppol routing, project or buyer reference, VAT treatment, retention and supporting attachments before sending. A PDF copy can aid readability but does not replace the required structured invoice where the obligation applies.

Preserve the audit trail

Keep the progress record, approval, event date, calculation, invoice version and delivery response together. Test a milestone approved after month-end, a disputed line and a credit correction. The system should not rewrite the original event merely to remove an overdue warning. Seek tax advice for the exact facts of the project.

Finally, make the workflow reviewable in daily operations. Assign an owner, record the official source and product version checked, and define when the decision must be reviewed again. A software flag is not legal advice, and an AI proposal is not approval. The authorised person must be able to see the customer, project, amounts, permissions and exceptions before confirming. Measure not only time saved but also ambiguous cases stopped safely. Update the instruction when regulation, contract terms, channels or product capabilities change. That discipline keeps the record useful to the site team, office, accountant and a later reviewer instead of turning today's configuration into an undocumented permanent rule.

Read the Belgian guidance on invoice timing and the official B2B e-invoicing FAQ. Explore Enfin, pricing, or discuss progress billing.