Correctly numbering your invoices is much more than a simple administrative formality; it's a fundamental pillar of your tax obligations as a freelancer or SME. The Spanish Tax Agency (AEAT) requires that numbering be sequential, without gaps, and ordered by date. An error in this area can create mistrust during an inspection and lead to problems.
In this article, we explain how to do it correctly and how new systems like VeriFactu will help you automate this process and ensure compliance.
The Golden Rule: Sequential and Unbroken Numbering
The Invoicing Regulation (Royal Decree 1619/2012) is clear: every invoice you issue must have a unique number that follows a sequential sequence. This means that if your last invoice was number 100, the next one must be 101. You cannot jump to 105, nor can you have two invoices with the same number.
Furthermore, the issue date of the invoices must also be sequential with their numbering. It is not valid to issue invoice 101 with today's date (July 5, 2026) and invoice 100 with tomorrow's date. This chronological order is crucial for the traceability required by the Tax Agency.
What if you make a mistake? If you make an error and leave a gap, you can't simply fill it in. The correct solution is to issue a credit note (rectifying invoice) to cancel the incorrect one and create a new one with the appropriate number.
When and How to Use Invoice Series
Invoice series are prefixes that allow you to maintain several sequential numbering sequences simultaneously. They are extremely useful and, in some cases, mandatory. You can create different series for:
* Different business lines: For example, `SERVICES-2026/001` for consulting and `PRODUCTS-2026/001` for material sales.
* Different establishments: If you have several stores, each can have its own series.
* Credit notes (rectifying invoices): It is mandatory to use a specific series for them. For example, `CN1-2026/001`.
* Specific operations: Such as invoices issued by the recipient or in bankruptcy proceedings.
Using series helps you maintain order and clarity in your accounting, facilitating both your internal management and a potential review by the AEAT.
The Arrival of VeriFactu: The End of Manual Errors
Manual management of numbering, especially with tools like Excel or Word, is a common source of errors. To prevent this and combat tax fraud, the VeriFactu system was approved. This system, which will be mandatory from January 1, 2027, for companies and from July 1, 2027, for freelancers and micro-SMEs, requires the use of adapted invoicing software.
These programs ensure that every generated invoice automatically meets the requirements for sequential and unbroken numbering. Additionally, they send a record of each invoice to the AEAT, making it impossible to manipulate them. If you want to better understand this new framework, you can check our guide on What is VeriFactu? Guide for Freelancers in Spain.
Adapting in advance is the best strategy. Knowing the deadlines will allow for a smooth and surprise-free transition. You can find all the details in our article on VeriFactu 2027: Deadlines for Freelancers in Spain.
In summary, maintaining impeccable invoice numbering is a key obligation. Although it has required manual discipline until now, the imminent arrival of VeriFactu will simplify the process, bringing security and peace of mind to your business.