Key takeaways
- An invoice must be issued no later than the fifteenth day of the month following the chargeable event (Royal Decree no. 1, art. 4).
- The clock starts at delivery or completion of the service, or earlier if you collect an advance payment.
- A periodic invoice can group a single customer's transactions falling within the same calendar month.
- The 2026 B2B mandate changes the invoice format, not the deadline to issue it.
Knowing when to issue an invoice is not an administrative nicety: it is a dated VAT obligation. In Belgium, the invoice issuance deadline is set by Royal Decree no. 1 of 29 December 1992, and it rests on a single rule, the fifteenth day of the following month. This article explains that rule, when its clock starts, and how a periodic invoice lets you group several transactions without missing the deadline.
The fifteenth-day rule
The principle fits in one sentence. Under article 4 of Royal Decree no. 1, the invoice must be issued "no later than the fifteenth day of the month following the one in which the chargeable event" of the tax occurred. In other words, you have the rest of the transaction month, plus fifteen days of the next month.
An example makes the mechanics concrete. You deliver goods on 8 March: the chargeable event falls in March, and you have until 15 April to issue the invoice. A service completed on 27 March follows exactly the same deadline, 15 April. The precise day of the transaction within the month does not bring the deadline forward: it is always the 15th of the following month.
The starting point: chargeable event and chargeability
Everything hinges on when the deadline starts. The chargeable event is the moment the transaction is legally carried out: for a supply of goods, it is the moment the goods are made available; for a supply of services, it is the moment the service is completed. That moment triggers the fifteenth-day clock.
One case moves that starting point: an advance payment. When you collect all or part of the price before delivery or completion, VAT becomes chargeable on that collection. Royal Decree no. 1 then requires the invoice to be issued no later than the fifteenth day of the month following the collection. An advance received on 20 February must therefore be invoiced by 15 March, even if the service has not yet taken place.
- 1
The chargeable event occurs
Day 0Delivery of the goods or completion of the service. Or, for an advance, collection of the price.
- 2
The transaction month runs
Month MYou can invoice at any time, without waiting.
- 3
Issuance deadline
15th of month M+1By the 15th of the following month at the latest, the invoice must be issued.
This distinction between the chargeable event and chargeability is not academic: it determines the VAT period the transaction belongs to, and therefore the return in which it must appear. Invoicing on time also means declaring the right transaction in the right period.
The periodic invoice: grouping a month of transactions
Issuing one invoice per delivery quickly becomes unmanageable when the same customer places several orders in a month. The law provides an answer: the periodic invoice. The EU directive (Directive 2006/112/EC, art. 223) allows a single invoice covering several separate supplies of goods or services, provided the VAT relating to those transactions becomes chargeable within the same calendar month.
In practice, a supplier who delivers the same customer on the 3rd, 12th and 26th of the month can combine those three transactions on one invoice. The issuance deadline is still governed by the fifteenth-day rule: the periodic invoice must go out by the 15th of the following month. You cut the number of documents without ever leaving the legal framework.
| Per-transaction invoice | Periodic invoice | |
|---|---|---|
| One invoice per delivery | ||
| Groups a month of a customer's transactions | ||
| Transactions chargeable in the same calendar month | ||
| Deadline on the 15th of the following month |
The obligation to issue: when an invoice is due
The deadline assumes an invoice is due in the first place. In B2B it almost always is: the VAT Code requires an invoice for supplies of goods and services made to another taxable person or to a non-taxable legal entity. In B2C the obligation is narrower and covers only specific cases, but nothing prevents you from issuing an invoice to a private customer who asks for one.
From 1 January 2026, invoicing between taxable businesses established in Belgium will have to take the form of a structured electronic invoice, exchanged over the Peppol network. This mandate changes the format and channel of the invoice, not the deadline to issue it: the fifteenth-day rule is unchanged. For the calendar and the exact scope, see Peppol in Belgium: the B2B mandate on 1 January 2026.
Invoice on time, without watching the clock
YouInv generates your compliant invoices, sends them over Peppol and keeps track of every transaction so nothing overruns the fifteenth day.
What a late invoice really costs
Issuing an invoice outside the deadline is a breach of VAT obligations and exposes you to an administrative fine. But the most concrete cost is often elsewhere. A customer's payment period runs from receipt of the invoice or the delivery: an invoice issued late is a collection delayed by the same amount. On an SME's cash flow, the effect is immediate.
A delay also weakens compliance. A March transaction invoiced in May risks attaching to the wrong reporting period, and disorderly invoicing complicates any audit. The fifteenth-day rule is not a trap: it is a cadence that, once kept, protects both your cash flow and your VAT return.
Further reading
- Mandatory invoice details in Belgium: what the invoice must contain, once the deadline is met.
- The advance-payment invoice in Belgium: rules and VAT: the treatment of an advance payment.
- Payment terms between businesses in Belgium: what happens after issuance.
The reference sources prevail: Royal Decree no. 1 of 29 December 1992 and Directive 2006/112/EC on the common system of VAT.
What is the deadline to issue an invoice in Belgium?
The invoice must be issued no later than the fifteenth day of the month following the one in which the VAT chargeable event occurred (Royal Decree no. 1 of 29 December 1992, art. 4). For a delivery on 8 March, the deadline therefore runs to 15 April.
When does the invoice issuance deadline start?
The starting point is the chargeable event: the delivery of the goods or the completion of the service. If you collect all or part of the price before that date, VAT becomes chargeable on collection, and the deadline is counted from that month.
Can several transactions be combined on one invoice?
Yes. A periodic invoice may cover several separate supplies of goods or services made to the same customer, provided the related VAT becomes chargeable within the same calendar month (Directive 2006/112/EC, art. 223).
What are the risks of invoicing late?
Issuing an invoice outside the deadline is a breach of VAT obligations and can trigger an administrative fine. A late invoice also delays the start of the customer's payment period and can misstate the VAT return for the period.
Does the 2026 B2B mandate change the issuance deadline?
No. The structured e-invoicing mandate between taxable businesses, applicable from 1 January 2026, changes the format and channel of the invoice, not the legal deadline to issue it: the 15th-day rule is unchanged.
