KSeF invoices in Poland: what is the National e-Invoice System and how does it work? [2026 Guide]

Poland is on the threshold of a digital revolution in invoicing. The National e-Invoice System (KSeF) will change the way businesses issue and receive sales documents. Although the system has been operating on a voluntary basis since 2022, it will become mandatory for the largest companies from 1 February 2026, with KSeF extending to all remaining taxpayers from 1 April 2026.

The Ministry of Finance confirms that these deadlines are final – technical work is progressing according to plan, and KSeF invoices will come into force despite calls from the accounting and business community for another postponement.

In this guide we explain what KSeF is and what it is for, how the national e-invoice system works, and answer the most frequently asked questions from businesses ahead of the KSeF implementation.

What is KSeF? Definition and fundamentals of the system

KSeF is a nationwide IT platform managed by the Ministry of Finance, used for issuing, transmitting, receiving and storing structured invoices. The KSeF system enables businesses to exchange electronic documents in a standardised XML format, eliminating traditional paper invoices and various forms of e-invoices. KSeF features functions for verifying the compliance of KSeF invoices with a specified template, assigning them a unique identification number, and securely archiving them for a decade.

A KSeF invoice – a new, structured standard

An invoice in KSeF is a structured invoice – a document in XML format compliant with the logical structure FA(3) defined by the Ministry of Finance. Every invoice issued in KSeF will be assigned a KSeF number, allocated automatically by the system. Importantly, the identifier assigned by the platform will not replace the invoice number assigned by the issuer, but will function as an additional identification element within the system.

The obligation to use KSeF forms part of the EU’s VAT in the Digital Age (ViDA) initiative, which aims to digitalise and tighten VAT settlements across the European Union. Similar systems are already in operation in Italy, Romania and other Member States, although many are postponing implementation deadlines – Latvia recently deferred its system to January 2028.

How does the National e-Invoice System work? The invoice issuance mechanism

1. Invoice flow in KSeF – from issuance to archiving

The process of issuing and transmitting KSeF invoices differs fundamentally from traditional invoicing. The issuer does not send the document directly to the recipient – an invoice submitted to KSeF goes first to the government platform, where it undergoes validation. The system verifies the compliance of the XML invoice file with the logical template, and upon successful verification assigns a KSeF number and generates an Official Acknowledgement of Receipt (UPO). Only then does the document become an invoice issued in KSeF. KSeF enables automated data processing, streamlining accounting in real time and eliminating the risk of manual errors.

The recipient does not receive the invoice by email or post – they must log in to KSeF or download the document automatically via integrated accounting software. All KSeF invoices are stored in the cloud for 10 years, eliminating the need for in-house archiving and protecting against loss of documents. This is one of the key features of the system that distinguishes KSeF invoices from previous electronic invoicing solutions.

2. How to issue an invoice in KSeF? Available options

Businesses can issue KSeF invoices in two primary ways. The first is to use the free KSeF Taxpayer Application (version 2.0, available from February 2026), which allows invoices to be issued directly in the system without additional tools. The second option involves purchasing and using accounting software integrated with KSeF via the KSeF API 2.0, enabling bulk submission of KSeF invoices directly from the company’s own system.

E-invoices in KSeF may be issued in interactive mode (individual documents) or batch mode (bulk issuance and submission of invoices). In the event of a KSeF failure on the taxpayer’s side – for example due to loss of internet access – an emergency offline24 mode is available, which allows invoices to be issued outside the system with subsequent submission to KSeF by the next business day. In the event of a failure on the tax administration’s side, the issuer may submit documents within a specified period (1 or 7 days) after the system is restored, without any legal consequences.

3. Authentication – the key to KSeF access

Access to KSeF requires one of the following authentication methods: a Trusted Profile or qualified electronic signature (for sole traders), a qualified electronic seal (for companies), a KSeF token (valid only until the end of 2026) or a KSeF certificate. Tokens and certificates are dedicated methods for automation – connecting existing IT systems to KSeF. Companies that do not use an electronic seal need to register a representative via form ZAW-FA in order to grant specific individuals authorisation to issue invoices in KSeF. This is particularly important for accounting firms that need to use KSeF on behalf of multiple clients simultaneously.

When does KSeF come into force? Mandatory system timeline

Mandatory KSeF will be introduced in stages under the Act signed by the President on 27 August 2025. In December 2025, the Ministry of Finance unequivocally confirmed that there are no plans to defer the deadlines – KSeF invoices will apply from 1 February 2026 for companies whose turnover in 2024 exceeded PLN 200 million, with all remaining businesses subject to the obligation to issue invoices in KSeF from 1 April 2026. Micro-entrepreneurs may issue invoices outside KSeF until the end of 2026, provided their total monthly sales do not exceed PLN 10,000 gross. Penalties and the full obligation to use KSeF invoices without exception will apply from 1 January 2027.

Transitional period – reliefs until the end of 2026

The legislator has provided a number of facilitations during the initial period. Businesses may continue to issue traditional paper invoices from fiscal registers up to PLN 450 with the purchaser’s NIP. Until the end of December 2026, no penalties will be imposed for errors in KSeF invoicing, allowing time to learn and adapt procedures. Importantly, from 1 February 2026, all businesses – regardless of when they themselves begin issuing KSeF invoices – will be required to receive documents from counterparties already using the system. This is a frequently overlooked aspect of the KSeF implementation that requires companies to prepare by February, even if their own obligation to issue invoices does not apply until April.

Who is subject to the obligation to issue invoices in KSeF?

KSeF applies to virtually all taxpayers conducting business in Poland. The obligation to use KSeF covers active VAT taxpayers in B2B transactions, VAT-exempt taxpayers (who issue invoices), companies of all legal forms, sole traders, and local government units. The KSeF system also covers certain foreign entrepreneurs with a fixed place of business in Poland, where sales are made through that place of business.

KSeF invoices for consumers – individuals not conducting business activity – remain voluntary. The issuer may decide whether to issue a B2C invoice in KSeF or in the traditional manner. Where an invoice is issued in KSeF, however, the business must agree with the consumer on the method of delivering the invoice. Issuance outside KSeF also applies to certain specific documents, such as single-journey tickets and motorway toll invoices. Flat-rate farmers may use the system only after submitting an appropriate declaration in KSeF. If a Polish taxpayer issues an invoice to a foreign counterparty without a Polish NIP, they must issue it in KSeF but additionally provide the purchaser with a visual representation outside the system – most commonly as a PDF with a QR code enabling verification of the document’s authenticity.

Benefits of KSeF implementation for businesses

Despite initial concerns about transitioning to the new system, the National e-Invoice System brings measurable benefits. Automation of document circulation means that KSeF invoices reach the recipient almost immediately after approval by the system. Free archiving eliminates the cost of in-house document storage – KSeF has a built-in cloud storing invoices for a decade. Businesses using KSeF can expect faster VAT refunds – reduced from 60 to 40 days for taxpayers using the system. Every invoice is assigned a KSeF number and permanently registered, eliminating the risk of loss or destruction of the document. The UPO confirms acceptance of the document by the Ministry of Finance, providing certainty of delivery. The system also increases trust in B2B relationships through real-time verifiability of every KSeF invoice, and limits the possibilities for tax fraud through central registration of all transactions.

How to prepare your company for KSeF in terms of payments and invoicing?

Preparing for the system requires a considered strategy. The first step is to check whether the company is subject to the obligation to issue KSeF invoices from 1 February or April 2026 – this depends on the level of turnover in 2024. The next step is to choose the authentication method – the most convenient solution for sole traders is the Trusted Profile, while companies should consider obtaining a qualified electronic seal, i.e. a KSeF certificate.

It is essential to verify whether the current accounting software supports integration with KSeF via the KSeF API 2.0. The Ministry of Finance provides a Demo test environment where KSeF invoice issuance can be tested without risk of errors in production. It is worth taking advantage of the free training sessions offered by tax offices as part of the “Wednesdays with KSeF” series – the final sessions are taking place in December 2025. The accounting team or external accounting firm must be trained in KSeF invoicing and emergency procedures. Arrangements should be made with counterparties regarding the method of providing KSeF invoice visualisations, particularly where these are foreign entities requiring documents outside the system. It is also worth preparing emergency procedures in case of failure – downloading certificates for offline24 mode in advance and ensuring that key employees know how to issue a KSeF invoice in atypical situations.

Summary – KSeF and the future of Polish business

The National e-Invoice System is the inevitable future of Polish business. KSeF invoices will be rolled out in stages within the next two months, which is why it is worth beginning preparations today. Testing in the voluntary version will help avoid problems when mandatory KSeF becomes a reality in February and April 2026. The Ministry of Finance unequivocally confirms that there are no plans for further deadline deferrals – despite calls from the accounting and business community, implementation of the system is progressing according to the adopted schedule.

Businesses should bear in mind that using KSeF with the appropriate authentication will be necessary not only for issuing but also for receiving invoices from counterparties. The system encompasses far more than simply issuing an invoice – it is a comprehensive change to accounting processes requiring IT system integration and team training in KSeF invoice handling.

Do you need support in preparing your company for the new regulations?

ALTO experts will help you navigate the KSeF implementation safely and answer all questions regarding the practical use of the KSeF invoice system in your organisation. Contact us to ensure a smooth system rollout and avoid problems at this critical moment in the digital transformation of Polish invoicing.

See our other articles in the KSeF series:

• 01. KSeF failure – what happens to the invoice issuance deadline? >>
• 02. Self-invoicing in KSeF. When is an invoice created, how to accept it and how to avoid errors? >>
• 03. Corrective invoices in KSeF – how to do it correctly? >>
• 04. Technical aspects of issuing and marking invoices – QR codes in practice >>
• 05. Delivering invoices within KSeF and outside KSeF – practical issues >>
• 06. What you need to know about the new FA(3) schema? >>
• 07. New obligations in JPK_VAT – a revolution in reporting ahead of KSeF implementation >>
• 08. What to do when a counterparty does not use KSeF? >>
• 09. Who does not have to use KSeF, and when? >>

FAQ – KSeF: frequently asked questions and answers

What are KSeF invoices and will they replace traditional invoices?

KSeF invoices are structured XML documents issued through the National e-Invoice System – a government IT platform managed by the Ministry of Finance. Unlike traditional paper invoices or PDFs, KSeF invoices must be saved in a specific XML format compliant with the FA(3) structure and undergo verification in the system before acquiring legal force. From 1 February 2026 (for companies with turnover above PLN 200 million) and from 1 April 2026 (for other taxpayers), KSeF invoices are set to become the target form of sales documents in B2B transactions. The system provides automatic archiving for 10 years and assigns each document a unique identification number together with an Official Acknowledgement of Receipt (UPO).

What about KSeF invoices for foreign companies?

All KSeF invoices from 1 February or April 2026 must also be issued to foreign counterparties where the transaction is subject to Polish VAT regulations. However, where the purchaser does not have access to the Polish system, the seller is additionally required to provide a visual representation of the invoice with a QR code. From 1 January 2027, there will also be an obligation to include the KSeF number in bank transfers for payments under the split payment mechanism.

Does the recipient HAVE to download the invoice from the system?

No. The obligation to use KSeF applies to issuance, not receipt. The purchaser may deduct VAT even without logging into the system, if they receive a KSeF invoice visualisation in another form from the counterparty. However, automatic downloading of invoices via accounting software integrated with KSeF greatly simplifies bookkeeping and eliminates the risk of lost documents. The KSeF Taxpayer Application 2.0 may be useful for smaller companies that do not have advanced software.

How does the offline24 emergency mode work?

Where a KSeF failure occurs on the taxpayer’s side – for example where the business loses internet access – the offline24 mode may be used. This solution requires the prior downloading of a special KSeF certificate from the system. KSeF invoices issued in this mode must be submitted to the system by the next business day. The system is not, however, intended for extended invoicing outside the platform – it is solely an emergency safeguard.

Does the KSeF system replace JPK_VAT?

No, these are two separate tools. KSeF is not used to settle VAT – it is a platform for issuing and transmitting invoices. Taxpayers will continue to submit JPK_V7 declarations, although in future the functionalities of KSeF may simplify this process through automatic population of data from KSeF invoices registered in the system. The tax administration will, however, have full visibility of transactions thanks to the centralisation of invoicing data.

What are the penalties for failing to implement the system?

Penalties for failure to issue KSeF invoices may amount to 100% of the VAT shown on the invoice, or 18.7% of the total amount due for each document not issued or incorrectly issued. Financial penalties will not, however, apply until 1 January 2027. Until the end of 2026, businesses may issue invoices outside KSeF within the permitted exceptions without any financial consequences – this is a transitional period without penalties, designed to give companies time to implement the system and learn the new procedures.