National e-Invoice System (KSeF) from February 1, 2026 in Poland – How to Prepare?

What is the Polish National e-Invoice System and How Does It Work?

The National e-Invoice System (Krajowy System e-Faktur in Polish or just KSeF in short) is a nationwide IT platform created by the Polish Ministry of Finance, used for issuing, sending, receiving, and storing structured invoices. The system has been operating in Poland since January 1, 2022, as an alternative to traditional invoicing methods, both electronic and paper. From February 1, 2026, the KSeF system will become mandatory for the largest companies, and from April 1 for all other VAT taxpayers. Paper invoices issued after this date will no longer be recognized as legal documents.

The process of issuing KSeF invoices includes verification of two key elements:

• Compliance of the document (XML file) with the mandatory e-Invoice template;
• Authorization of the person sending the file.

After the invoice is sent by the seller, the system assigns it a unique identification number, and the document automatically becomes available to the recipient directly in the system.

The Polish National e-Invoice System and Structured Invoice: XML Format and FA(2) / FA(3) Structure

Structured invoices in KSeF are accepted only in XML format, compliant with a specified logical structure. Currently, the FA(2) structure is in force, published in the Central Repository of Electronic Document Templates (CRWDE) and introduced on September 1, 2023. From February 1, 2026, it will be replaced by a new logical structure FA(3).

The FA(3) structure, developed with input from entrepreneurs and experts, was published on June 25, 2025. The new FA(3) structure will completely replace the previous FA(2) version and will be mandatory for all invoices issued from February 1, 2026. This means that after this date, the KSeF system will no longer accept documents in the FA(2) format. Entrepreneurs should ensure their accounting software is updated to the latest version of the structure to avoid errors when submitting invoices to the system.

The FA(3) structure consists of four main elements:

1. Header;
2. Data of entities appearing on the structured invoice;
3. Detailed invoice data;
4. Footer.

Importantly, if an invoice is issued in FA(3), it is possible to add an attachment to the invoice, but this requires prior notification to the e-Tax Office (e-US).

The Role of the National e-Invoice System Number in Poland and UPO

Issuing electronic invoices in the KSeF system automatically assigns the document a unique identification number after acceptance, usually containing the seller’s VAT identification number (NIP), although there are exceptions.

Equally important is the Official Receipt Confirmation (Urzędowe Poświadczenie Odbioru or UPO in short in Polish), which serves as electronic proof of correct document submission. UPO functions similarly to a “return receipt” known from traditional postal correspondence. The document contains a reference number, date and time of submission, status, and a system signature. Only receiving the UPO along with the KSeF number confirms the formal issuance of the invoice.

Obligation to Use the National e-Invoice System in Poland – From When and Who Does It Concern?

The Act introducing the obligation to issue invoices in the National e-Invoice System in Poland specifies a precise schedule for the mandatory use of the system. The legislator took into account the size of enterprises, granting smaller entities more time to adapt to the new requirements.

A key fact is that receiving structured invoices in the National e-Invoice System will be mandatory for all entrepreneurs from February 1, 2026.

KSeF Implementation Schedule: February 1, 2026 – Large Entities (Turnover > PLN 200 million)

According to the regulations, the first stage of mandatory invoicing in the National e-Invoice System will cover the largest economic entities in Poland. From February 1, 2026, the system will be mandatory for companies whose gross sales value (including VAT) exceeded PLN 200 million in 2024. These enterprises will have to fully switch to issuing structured invoices in the system.

It is worth noting that the largest companies have a relatively short time to adapt their accounting systems and internal procedures. However, the obligation to issue invoices will be introduced gradually, and the obligation to receive structured invoices will cover all entrepreneurs from February 1, 2026.

KSeF Implementation Schedule: April 1, 2026 – Other VAT Taxpayers

The second stage of implementation will begin on April 1, 2026, and will cover all other VAT taxpayers – both active and those exempt from VAT. From the second quarter of 2026, all standard B2B invoices will be issued exclusively via the National e-Invoice System.

The regulations specify that this obligation concerns:

• Medium and small enterprises;
• Active VAT taxpayers;
• Entrepreneurs exempt from VAT (both due to low turnover and due to exempt sales);
• Taxpayers identified in Poland under the special EU OSS procedure with a Polish VAT number.

KSeF Implementation Schedule: January 1, 2027 – Micro-entrepreneurs (Turnover < PLN 10,000/month)

The last stage of implementation is planned for January 1, 2027. It concerns the smallest taxpayers meeting the criteria of so-called “digital exclusion.” The regulations define this group as entrepreneurs whose:

• Individual invoices do not exceed PLN 450 (equivalent to a simplified invoice);
• Total monthly gross sales value does not exceed PLN 10,000.

For the smallest entities, a special solution is provided. They may continue issuing electronic invoices (e.g., PDF) or paper invoices until the end of 2026, provided they do not exceed the monthly gross sales limit of PLN 10,000.

Penalties for Failure to Implement the National e-Invoice System in Poland

In 2026, entrepreneurs do not have to fear penalties for not implementing the National e-Invoice System, as this period will be treated as a transition phase and a so-called “soft launch” of the system. Only from January 1, 2027, tax authorities will be able to impose financial sanctions for non-compliance with the obligation to use the system. Entrepreneurs who do not comply with the new requirements may be fined up to 100% of the VAT amount shown on the invoice or 18.7% of its gross value.

Amount of Penalties

The amount of penalties will depend on the type of offense:

• Up to 100% of the VAT amount shown on the invoice – for failure to issue the invoice in the system;
• Up to 18.7% of the gross invoice value – when VAT is not shown on the invoice;
• Up to PLN 1,000 – in case of delayed submission of the invoice.

These penalties will be imposed by decision of the head of the tax office, so it is crucial to prepare the company properly and integrate accounting systems with the system before February 2026.

How to Prepare Your Company for the Polish National e-Invoice System Before 2026?

Successful implementation requires a systematic approach and starting preparations well in advance. Entrepreneurs who begin adapting their systems and procedures now will avoid technical problems during mandatory implementation.

Integration of Accounting System with the System API

The system API (Application Programming Interface) is a set of detailed rules and technical specifications defining the method of data exchange between the National e-Invoice System and external financial-accounting systems. This solution eliminates the need to log in to the Ministry of Finance’s platform each time – the entire process of issuing and downloading invoices runs automatically.

On June 30, 2025, the Ministry of Finance published detailed technical documentation for the API 2.0 along with integration support tools. The documentation includes, among others:

• Descriptions of methods, data structures, and parameters;
• Specification in Open API standard;
• SDK libraries in Java and .Net languages.

Small companies issuing up to 10-20 invoices per month can use free tools from the Ministry of Finance. Enterprises handling a larger number of documents will need to integrate their sales system with the system.

Employee Training on e-Invoice Handling

New procedures also require proper team training. The Ministry of Finance has planned practical training sessions in each of the 400 tax offices and launched the “Wednesdays with the System” program – a series of free training sessions starting September 24, 2025.

Trainings cover topics such as:

• Basic information about the system;
• Authentication and authorization;
• Issuing and receiving structured invoices;
• Handling free tools.

Employees should be trained in issuing e-invoices, offline mode operation, and verifying document correctness.

Verification of Contractors’ Data and VAT Number (NIP)

Before issuing an invoice, it is necessary to check whether the contractor has an active VAT identification number (NIP) and is registered as an active or exempt VAT taxpayer. The system automatically verifies the correctness of submitted invoices, and the most common error is inconsistency of NIP or contractor data.

The system also checks the consistency of NIP and business form with the VAT taxpayer registry. Incorrect data causes automatic rejection of the invoice. Verification can be done in the CEIDG database, the EU VAT register (VIES system), and the VAT white list.

Granting Permissions in the National e-Invoice System in Poland

The system is based on a credential model, which means each user must be authenticated and authorized. Permissions include:

• Issuing or accessing structured electronic invoices;
• Issuing structured invoices under self-billing;
• Granting, changing, or revoking permissions.

Permissions can be granted electronically via the interface software (ksef.mf.gov.pl) or in paper form by submitting the ZAW-FA notification. Permissions can be assigned fully to one person or divided among several.

ZAW-FA Notification to the Tax Office

The ZAW-FA form (Notification of Granting or Revoking Permissions to Use the Polish National e-Invoice System (KSeF)) is necessary for legal entities that do not have a qualified electronic seal. Sole proprietorships receive access to the system account automatically, without additional documents.

The completed ZAW-FA form must be submitted to the competent head of the tax office, indicating the person receiving ownership permissions. According to the system usage regulation from 2021, the notification can only be delivered in paper form – in person or by mail.

Access is usually granted within 2 working days from submitting ZAW-FA. Note that the notification concerns the production version of the system, whose documents have real tax effects.

Changes in Invoicing Process After Implementation

Mandatory introduction means significant changes in daily invoicing processes. Entrepreneurs must prepare for new rules affecting both accounting procedures and document circulation in the company.

No More Duplicate Invoices

The concept of invoice duplicates will completely disappear from the Polish economic circulation after the system becomes mandatory. Moreover, the system acts as a central database, so invoices cannot be lost. Each invoice accepted by the system receives a unique registration number and remains accessible there.

The buyer will be able to download the invoice from the database at any time – even 10 years after issuance. This solution eliminates bureaucracy related to issuing duplicates and simplifies archiving processes.

Corrections Only via Corrective Invoices

The Polish National e-Invoice System (KSeF) does not allow editing or canceling an already issued invoice. The only way to correct an error will be to issue a corrective invoice. This rule applies to all errors that can currently be corrected by credit notes.

A particularly complicated procedure is correcting an incorrect buyer’s NIP number. In this case, two actions are required:

• Issuing a corrective invoice “to zero” with the incorrect NIP;
• Issuing a new original invoice with the correct buyer’s NIP.

Obligation to Use QR Codes on Invoice Visualizations

All invoice visualizations issued must be marked with QR codes that allow verification of the document’s authenticity. The code enables checking whether the invoice was actually issued in the system and whether the data contained is correct.

Invoices issued online and delivered to the buyer outside the Polish National e-Invoice System (KSeF) require a single QR code with the invoice identification number. Offline invoices must contain two QR codes:

• The first marked “OFFLINE”;
• The second labeled “CERTIFICATE”.

Generating the second code requires a certificate, available from November 1, 2025.

No Credit Notes and PDF as Original

From February 1, 2026, entrepreneurs will no longer be able to issue credit notes – every change on the invoice will require a corrective invoice issued by the seller. The system does not allow editing or canceling documents after submission, so error correction will only be possible by issuing a new corrective invoice.

The original invoice is exclusively the XML file stored in the system. PDF versions may only serve as copies for the contractor. Companies should update their invoicing procedures and train staff to avoid errors after the new rules come into force.

Exceptions, Failures, and Offline Mode

Regulations provide a number of exceptions and emergency solutions to ensure business continuity when the system is not operational. Understanding these mechanisms is key to proper company functioning after mandatory implementation.

Offline24 Mode and System Failures

Offline24 mode allows issuing invoices outside the Polish National e-Invoice System in emergencies or when there is no internet access. The invoice issued in this mode must be sent to the National e-Invoice System in Poland no later than the next business day after issuance. The Ministry of Finance does not require justification for using this solution, simplifying procedures.

In the event of an officially announced failure, invoices can be issued in emergency mode. The obligation to submit documents then is 7 business days after the failure ends. If a total failure is announced in public media, paper invoices and electronic invoices can be issued without later submission.

No Obligation to Include System Number in Transfers Until December 31, 2026

The obligation to include the system number in payment titles has been postponed until January 1, 2027. Entrepreneurs thus gain an additional year to adapt accounting, banking systems, and settlement processes. From January 1, 2027, the number will be required both in standard transfers and in the split payment mechanism (MPP).

Benefits of the National e-Invoice System in Poland

Although the mandatory KSeF system is a controversial topic, it cannot be ignored that it brings many advantages. Benefits of the National e-Invoice System in Poland include:

1. Accounting automation – invoices in XML format can be automatically imported and posted to ERP systems;
2. Faster tax settlements – data is immediately available to offices, accelerating VAT refunds;
3. Document security – invoices are stored in the system for 10 years, eliminating the risk of loss or destruction;
4. Continuous access to invoices – both the issuer and the buyer can download the document from the system at any time;
5. Fewer errors – the structure of a structured invoice prevents the issuance of a document with incorrect data (e.g., incorrect Tax Identification Number (NIP), incorrect VAT rates);
6. Easier auditing and compliance – invoices are immediately visible to the tax administration;
7. Time and cost savings – no need to send invoices by email, print them, or archive them in paper form;
8. Unified invoice format – one standard for all businesses in Poland;
9. No obligation to keep copies – archiving in the National Securities and Exchange Office replaces company digital archives;
10. Easier verification of contractors – the system confirms the existence and status of a VAT payer.

Drawbacks of the National e-Invoice System in Poland

On the other hand, many disadvantages of the KSeF system are already apparent, including:

1. Implementation costs – the need to update or integrate accounting software with the KSe API;
2. Technical complexity – smaller companies may have difficulties configuring the system and handling XML files;
3. Required training – employees must learn new procedures, formats, and authorization rules, which generates costs and requires the employee to devote their time;
4. Lack of flexibility – an issued invoice cannot be edited or canceled, and corrections require the issuance of a correction invoice;
5. Dependence on the Ministry of Finance system – in the event of a system failure or overload, invoicing is difficult;
6. Requirement to use QR codes – an additional technical requirement for invoice visualization;
7. Format limitations – after February 1, 2026, PDF invoices will not be recognized as originals, forcing a change in practices;
8. Risk of integration errors – incorrect implementation may result in invoice rejection by the system;
9. Requirement of internet access and electronic signature – problematic in some industries or field situations.

The National e-Invoice System (KSeF) implementation in Poland - Summary

To safely transition to mandatory e-invoicing, it's important to ensure your sales and accounting system supports KSeF invoices, your team understands the processes, and your customers are ready to receive structured invoices. This will ensure your electronic invoice passes KSeF verification without errors, and your company will benefit from faster settlements and full compliance from day one.

If you need support with KSeF implementation, contact our team! Evotax specialists are happy to assist, and our services include accounting or HR and payroll services.