How long should I wait before sending a formal notice for an unpaid invoice in Belgium?

There is no statutory minimum delay before sending a formal notice, but it is advisable to send at least one friendly reminder first. In practice, most Belgian SMEs wait between 30 and 60 days after the due date. Acting too quickly can damage the business relationship, while waiting too long reduces your chances of recovery.

Does a formal notice for an unpaid invoice have to be sent by registered mail in Belgium?

Belgian law does not require registered mail for every formal notice, but contracts or general terms may stipulate it. In practice, sending by registered mail with return receipt — on paper or as a qualified eRegistered — is strongly recommended, as it provides essential proof of receipt if court proceedings become necessary.

What late-payment interest can I claim for an unpaid B2B invoice in Belgium?

For B2B receivables, the Belgian law of 2 August 2002 on late payments allows you to claim interest at the commercial legal rate (published every six months in the Belgian Official Gazette) and a flat-rate collection indemnity of at least 40 €. These rights apply by operation of law, without any need to include them in the contract.

Can a formal notice be sent by email in Belgium?

An email can qualify as a formal notice if the recipient acknowledges receipt and the contract does not impose another form. In practice, proving receipt of a plain email is difficult. For a formal notice with full evidentiary value, a qualified eRegistered or bpost registered mail with return receipt remain the safest options.

What does it cost to send a registered formal notice in Belgium?

A standard bpost registered letter with return receipt costs between 7 and 9 € depending on format and weight. Online mailing solutions such as Bjet24 also allow you to send a registered letter without visiting a post office, from a few euros, with archived proof of sending.

Unpaid invoice dunning in Belgium: 3 templates for SMEs

The right dunning path in Belgium

The vast majority of unpaid invoices are settled before reaching court. The difference is not made by an aggressive first letter — it is made by the consistency of the path. In Belgium, the sequence that works for 80% of cases comes down to three letters:

a friendly reminder one to two weeks after the due date,
a firm second reminder a few weeks later,
a formal notice sent by bpost registered or eRegistered mail.

Each letter has a clear role: preserve the relationship at first, ramp up the pressure progressively, then trigger legal consequences if nothing moves.

Template 1 — Friendly reminder (D+10 to D+15)

Neutral tone, oversight assumption, no accusation. Sent by email or simple letter depending on your customer relationship.

Subject: Reminder — invoice no. [xxx] dated [date]

Hi [Firstname],

Save error on our side, invoice no. [xxx] dated [date]
for an amount of [amount] € is still open today.

It is probably an oversight. Could you settle it by
[date + 7 days] at the latest?

If there is any difficulty, please reach out — we will
find a solution.

Best regards,
[Name]

Template 2 — Firm second reminder (D+30)

More directive tone, reminder of the due date, contractual penalties and announcement of the next step.

Subject: Second reminder — invoice no. [xxx] still unpaid

Dear Sir or Madam,

Despite our reminder of [date], invoice no. [xxx] for
[amount] € remains unpaid today. As a reminder, our
general terms provide for late-payment penalties at
[x %] and a flat-rate indemnity in accordance with the
law of 2 August 2002 on late payments.

We ask you to proceed with payment within
[10 calendar days]. Failing this, we will have to
send you a formal registered notice.

Best regards,
[Name]

Template 3 — Formal notice (D+45 to D+60)

This letter must go out by bpost registered with return receipt or as a qualified eRegistered. It opens the legal deadlines and forms essential proof should you need to go further. For all required mentions, see our full formal notice guide for Belgium.

Subject: Formal notice — invoice no. [xxx]
Sent by registered mail with return receipt

Dear Sir or Madam,

We note that invoice no. [xxx] dated [date] for an amount
of [amount] € remains unpaid despite our previous
reminders.

By this letter, we formally put you on notice to proceed
with the payment of this sum within a period of 14
calendar days from receipt of this letter.

Failing payment within this deadline, we will claim
late-payment interest at the legal rate together with a
flat-rate collection indemnity, and will entrust the file
to our counsel or to a bailiff, the whole at your expense.

Yours faithfully,

[Name and position]

The legal rules (B2B)

For receivables between businesses, the Belgian late-payment law allows you to claim, without any specific contractual clause:

late-payment interest at the commercial legal rate,
a flat-rate collection indemnity (at least 40 € at the time of writing),
the reasonable costs incurred to recover the debt.

Also check the maximum payment terms imposed by law when facing an SME or a public administration: they cap what you can include in your general terms.

Which channel at each step

Friendly reminder: email or simple letter. Preserves the relationship.
Second reminder: email + simple letter, or letter alone if the client does not read their mail. No registered required.
Formal notice: bpost registered with return receipt (paper) or qualified eRegistered (if the client is a business with active eBox). This is the letter that opens your deadlines.

No point in sending a registered letter from the first reminder: it costs 7 to 9 € and carries no extra legal weight at that stage. Keep it for the formal notice, where it actually matters.

How Bjet24 automates this path for an SME

The hidden cost of collection is not the stamp — it is the time spent preparing, printing, posting and following up. With Bjet24, your accounting software or ERP directly triggers the right letter at the right moment:

friendly reminder by email,
second reminder as a simple letter, printed and posted,
formal notice as bpost registered or eRegistered, with proof archived in the customer file.

All without a team member leaving their desk. SMEs sending regular dunning correspondence can learn more about professional bulk mailing for Belgian SMEs. Check our online letter sending pricing to estimate the cost of an automated dunning workflow.

Three tips that change collection rates

Send the first reminder fast. A reminder at D+10 is read and paid far more often than one at D+45.
Stay factual. Early threatening letters scare off good payers and do not impress bad ones.
Keep your cadence. What works is regularity — not occasional outbursts.

Summary

A good Belgian dunning path is three well-dosed letters with a registered formal notice to close the sequence. Put the process in place once, automate it with Bjet24, and you will recover the majority of unpaid invoices without ever touching court.