Common Invoicing Mistakes Contractors Should Avoid

Apply the Correct VAT Rate

Belgian contractors must verify whether the reduced 6 % VAT rate applies (e.g., residential property older than 10 years, private use, signed declaration). Check the three conditions for each project and record the decision in your files before issuing the invoice.

Obtain the VAT Declaration Form in Advance

The reduced‑rate declaration must be signed by the client before work starts. Keep a copy and have the client sign at the first site visit. A signed form is needed to demonstrate eligibility for the lower rate if the tax authorities request evidence.

Invoice Promptly After Completion

Issue the invoice as soon as the work is finished, ideally the same day or within the same week. Prompt invoicing reduces the time between service delivery and payment.

Send Payment Reminders Systematically

If a payment is overdue, send a courteous reminder a few days after the due date. Follow up with a second reminder after about two weeks, mentioning the statutory interest rate, and a third reminder after a month, indicating possible formal notice.

Use Clear, Detailed Descriptions

Each invoice line should mirror the corresponding quotation: describe the work, quantity (hours, square metres, units), unit price, and applicable VAT rate. This transparency helps the client understand the charge and simplifies bookkeeping.

Keep Sequential Invoice Numbers

Belgian law requires consecutive invoice numbers without gaps or duplicates (e.g., 2026‑001, 2026‑002, …). Gaps may raise questions during a tax audit. Use accounting or invoicing software that automatically generates the next number to maintain compliance.

Separate Change Orders from the Main Invoice

When additional work is performed, issue a separate change‑order document and reference it on the invoice (e.g., “Change order dated 12/03/2026: relocate bathroom drain, €1 200 excl. VAT”). This prevents surprise totals and makes it easier to justify extra charges.

Build a Structured Invoicing Process

Implement a simple workflow that includes:

• A pre‑project checklist for VAT eligibility and required declarations.
• A standard template that matches quotations line‑for‑line.
• Automated reminder settings in your invoicing tool.
• Automatic sequential numbering.

Checklist for Each Project

1. Verify VAT rate eligibility (standard or reduced).
2. Obtain signed VAT declaration form before work starts.
3. Use the approved invoice template; copy quotation line items exactly.
4. Assign the next sequential invoice number.
5. Issue the invoice promptly after completion.
6. Record any change orders separately and reference them.
7. Schedule reminder emails according to the overdue timeline.

Further resources

• Information on Belgian e‑invoicing requirements (effective 1 January 2026): e‑invoicing in Belgium
• Current VAT rules and guidance: VAT for enterprises – verify your specific situation.