Accounting for self-employed professionals in Luxembourg: invoices, expenses, VAT and CCSS

The four flows a self-employed professional should keep under control

Good accounting is not just a year-end exercise. It starts with consistently organising what comes in, what goes out and the evidence behind each movement.

What accounting obligations apply to a sole proprietor?

Guichet.lu states that sole proprietors must keep transparent accounts, including records showing money coming in and going out. The exact obligations depend on factors such as the activity, merchant status and turnover.

For businesses subject to the general accounting rules, entries must be chronological, complete, accurate and made without delay. Accounting documents are generally kept for 10 years.

For a sole trader operating as a merchant with annual turnover above EUR 100,000 excluding VAT, Guichet.lu provides for more formal accounting requirements, including use of the standard minimum chart of accounts. Confirm the exact requirements for your legal and business situation.

Correct invoicing is the first layer of good accounting

An invoice is more than a document sent to a customer. It is accounting evidence and forms part of the VAT audit trail.

• Use a unique sequential invoice number.
• Clearly identify the supplier, customer, date, nature of the supply and amounts.
• Include the required VAT information when tax is due, or the appropriate reason where it is not.
• Keep a copy of every issued invoice and connect it to the related payment.

Business expenses: organisation matters as much as the expense

A robust workflow keeps supporting evidence for every expense and links it to the related payment. A bank transaction alone does not always explain the business purpose, supplier or VAT treatment of a cost.

1. 1
   Collect the invoice or receipt at the time of purchase.
2. 2
   Classify the expense consistently.
3. 3
   Match it to the corresponding bank movement.
4. 4
   Keep the document and relevant information for the required period.
5. 5
   For mixed private/business use or unusual treatment, obtain professional review.

VAT should not be managed separately from your accounts

If you are under the regular VAT regime, client invoices, supplier invoices and accounting entries directly influence your VAT position. If you use the small-business exemption, the invoicing and deduction rules are different.

Since 2025, Luxembourg’s national SME VAT exemption threshold is EUR 50,000 of annual turnover, subject to the statutory conditions. For the full explanation, see our Luxembourg VAT guide.

CCSS: why your accounting income also matters for social security

Self-employed social-security contributions are calculated from professional income. Depending on the situation, the CCSS first works with a provisional income and later recalculates when the Luxembourg Inland Revenue communicates the final income.

Keeping your accounts current therefore also helps you estimate professional income more accurately and reduce the risk of a large gap between provisional contributions and the final adjustment. See our CCSS guide for self-employed professionals.

A practical monthly routine

1. 1
   Issue and review all client invoices for the month.
2. 2
   Collect supplier invoices and other supporting evidence.
3. 3
   Import or review bank movements and match them.
4. 4
   Identify unpaid invoices and expenses missing evidence.
5. 5
   Review your VAT position where applicable.
6. 6
   Compare actual income with your CCSS estimate when the business changes materially.
7. 7
   Carry out a deeper review with your accountant or fiduciaire when needed.