1. What is KSeF?

The National e-Invoice System (KSeF) is an IT system used specifically for:

• issuing, receiving, accessing, and storing structured invoices, and
• granting or revoking authorizations to use KSeF.

KSeF automatically assigns a unique identification number to each invoice issued.

To start using KSeF, authentication in the system is required. Authentication can be done by the entrepreneur or a person or entity designated by the entrepreneur. Implementing regulations specify possible methods of authentication in the system (e.g., using a Trusted Signature, a qualified signature or a qualified seal).

2. Deadlines

The obligation to issue invoices in KSeF, in accordance with the currently processed draft of the KSeF 2.0 Act, will take effect on:

• 01.02.2026 for entrepreneurs whose sales value (including tax) exceeded PLN 200 million in 2024,
• 04.2026 for other entrepreneurs.

All invoices in B2B transactions between VAT taxpayers registered in Poland will be sent and received exclusively through KSeF. Issuing VAT invoices through KSeF will be the only acceptable form of invoicing in Poland. And this means that all VAT taxpayers (active and exempt) will be required to issue structured invoices, i.e. in xml format compliant with the logical structure of the FA(2) e-Invoice published in the Central Repository of Electronic Document Templates (CRWDE) on the ePUAP platform.

IMPORTANT:

The Ministry of Finance plans to release a test version of the KSeF 2.0 Taxpayer Application starting in November 2025, so that all entrepreneurs can familiarize themselves with the system’s solutions and functionalities.

3. KSeF number vs. invoice number

KSeF number is a unique number that identifies an invoice in the National e-Invoice System (KSeF). It is assigned automatically by the system after the e-invoice has been successfully sent to the IT environment. This number is returned in the UPO (Official Certificate of Receipt) and is not itself part of the xml file.

However, the number in the KSeF system will not be the same as the invoice number. Importantly, KSeF does not dictate the format of the invoice number. This means that taxpayers will apply, with regard to the numbering of invoices, the principle referred to in Article 106e of the Value Added Tax Act, which stipulates that an invoice should contain a consecutive number assigned within one or more series, which uniquely identifies the invoice.

IMPORTANT:

The number in KSeF will therefore not be the invoice number. This means that taxpayers will be able to continue to use the existing method of numbering invoices. However, it is important that the numbering remains continuous, unambiguous and consistent – in accordance with the provisions of the Value Added Tax Act.

4. Invoice with attachment

According to the Ministry of Finance, as of 01.02.2026, an additional functionality will be introduced, allowing the submission of invoices with attachments to KSeF. Submitting an invoice with an attachment to KSeF will not be mandatory. The attachment will constitute an integral part of the invoice. It may include the obligatory elements of the invoice, specified in Article 106e sec. 1 of the Value Added Tax Act, as well as closely related data. Marketing information cannot be included in an attachment. A structured invoice is sent in the form of an xml file, and the attachment will be its element (an additional node of the FA structure). Therefore, it is not possible to send an attachment to KSeF in any format other than an xml file, such as a pdf file. In other words, KSeF will not accept files in unstructured form, such as pdf or jpg – these types of attachments (pdf, jpg, etc.) will still be able to be sent outside of this system.

IMPORTANT:

The functionality of sending an invoice with an attachment will be available after the taxpayer submits the appropriate notification in the e-Tax Office service. Taxpayers will be able to submit these notifications starting from 01.01.2026.