National System of e-Invoices: Krajowy System e Faktur (KSeF)

What is KSeF?

In Poland, KSeF (Krajowy System eFaktur) is the official national system of e-Invoices. The System efaktur is administered by the head of the National Revenue Administration of Poland. The KSeF is a central government platform and actually an IT system that is used for the issuance, reception, and storage of electronic invoices. All issued invoices will have to be declared through system KSeF. The XML file must be signed before being sent to KSeF Faktury, then sent to the government portal. So, companies must send all electronic invoices to the KSeF, and a digital time stamp will be applied to invoices there. KSeF also conducts analysis, validation, and control of the validity of the data in received invoices. In addition, the platform issues a series of notifications that will inform users about invoice rejection or the inability to issue invoices in situations the KSeF platform is not working.

KSeF 2026: What the December 2025 Implementing Regulations Change in Practice

The publication of four implementing regulations in December 2025 marks a decisive turning point in Poland’s National e-Invoice System (KSeF). While earlier legislative amendments clarified when KSeF would become mandatory, these regulations finally explain how the system will operate in practice and where its boundaries lie.

Rather than introducing new policy objectives, the December 2025 regulations address long-standing technical, procedural, and reporting uncertainties that had remained unresolved following repeated postponements of mandatory KSeF. Taken together, they establish a comprehensive operational rulebook for 2026 and beyond, covering scope exclusions, simplified invoices, system usage rules, and the alignment of KSeF with JPK_VAT reporting.

This article analyzes these four regulations and explains what they change from a practical compliance perspective.

Executive Summary: From Legal Framework to Operational Certainty

Until recently, KSeF discussions focused primarily on timelines and system readiness. The December 2025 regulations shift attention decisively toward execution. By clarifying when structured invoices are not required, how simplified invoices must be handled, how KSeF is used on a day-to-day basis, and how invoice data feeds into VAT reporting, the Ministry of Finance has closed many remaining interpretative gaps.

For taxpayers, this signals that KSeF compliance is no longer a future-state consideration. The operational rules are now largely fixed, and preparation must move from planning to implementation.

Limited Scope Exemptions: When Structured Invoices Are Not Required

One of the most anticipated regulations, issued on 7 December 2025, specifies cases in which there is no obligation to issue structured invoices through KSeF. Importantly, this regulation does not create a general opt-out. Instead, it identifies narrowly defined scenarios where issuing a structured invoice is technically infeasible or incompatible with existing documentation models.

These cases include, among others:

• Toll motorway services documented by receipts recognized as invoices
• Passenger transport services documented by tickets treated as invoices
• Certain aviation supervision and route-charge services
• Financial and insurance services exempt from VAT and documented using simplified invoices with limited data
• Specific self-billing scenarios involving foreign entities that do not use a Polish Tax Identification Number

The underlying rationale is technical. KSeF invoices must follow the structured template defined in Article 106gb(8) of the VAT Act. Where documents such as tickets or insurance records cannot be generated in this format, the obligation to issue a structured invoice does not apply.

These exclusions should therefore be understood as technical exceptions, not policy flexibility. They do not weaken the overall obligation to use KSeF and should not be interpreted expansively.

Self-Billing and Foreign Entities: Clarifying a Long-Standing Uncertainty

The same regulation clarifies self-billing scenarios involving foreign entities that do not use a Polish Tax Identification Number. Under the clarified rules, a foreign buyer identified for VAT purposes in another EU Member State may issue invoices in KSeF under self-billing arrangements for intra-Community supplies, even if that buyer does not hold a Polish NIP for that activity.

This clarification is particularly relevant for multinational groups operating centralized invoicing or self-billing models. It reduces uncertainty around cross-border compliance while preserving KSeF’s role as a national control mechanism.

Simplified Invoices After February 2026: What Actually Changes

A second regulation issued on 7 December 2025 amends the rules on issuing invoices, focusing specifically on simplified invoices and VAT-exempt transactions.

From 1 February 2026, a clear distinction applies:

• Simplified invoices issued through KSeF must include the issuer’s Tax Identification Number (NIP).
• Simplified invoices issued outside KSeF, such as those provided directly to consumers, may continue to follow existing rules without the issuer’s NIP.

Where the buyer uses a Tax Identification Number, that number must also be included on the simplified invoice.

This distinction reinforces an important compliance principle: once an invoice is issued through KSeF, it falls fully within the system’s identification and traceability framework. Simplification of invoice content does not imply reduced control when KSeF is used.

The Core Operational Rulebook: Regulation on the Use of KSeF

The regulation issued on 12 December 2025 on the use of the National e-Invoice System forms the operational backbone of KSeF. Rather than redefining policy objectives, it translates statutory concepts into enforceable procedures.

Key areas covered include:

• Types of authorizations and procedures for granting and withdrawing them, including the ZAW-FA notification template
• User authentication methods, including the use of KSeF certificates
• The scope of data required to access invoices without additional authentication
• Rules for marking invoices sent to KSeF and made available outside the system
• Procedures and technical requirements for issuing invoices with attachments

This regulation replaces the earlier 2021 framework and reflects the transition from voluntary to mandatory use. Its provisions are closely aligned with the technical documentation published by the Ministry of Finance, reinforcing consistency between legal rules and system behavior.

Invoice Marking, OFFLINE Modes, and Audit Traceability

A particularly significant part of the regulation concerns invoices issued outside KSeF due to system unavailability or approved offline scenarios. Such invoices are not treated as informal documents.

They must be clearly marked using defined verification codes, identifiers, and—in certain cases—the explicit “OFFLINE” designation. QR codes and linking mechanisms ensure that invoices issued outside the system can later be verified within KSeF once transmitted.

The regulatory logic is clear: audit continuity must be preserved. Offline issuance is an exception to the transmission method, not to compliance obligations.

Invoices with Attachments: A Controlled Extension of KSeF

For the first time, taxpayers are permitted to issue invoices with attachments through KSeF, subject to strict procedural and technical conditions. Prior notification to the tax authority is required, and confirmation must be obtained before such invoices can be issued.

Attachments are limited to one per invoice and may not exceed 3 MB in total size. The attachment forms an integral part of the invoice and must meet defined technical standards.

This approach balances practical business needs—particularly in sectors requiring supporting documentation—with the need to prevent uncontrolled expansion of invoice content within KSeF.

JPK_VAT and KSeF Numbers: Closing the Reporting Loop

The fourth regulation, also issued on 12 December 2025, amends the JPK_VAT file with declaration to align VAT reporting with KSeF.

Under the amended framework, the KSeF invoice number becomes a central reference in sales and purchase records. Specific markers distinguish invoices issued offline without a KSeF number at the reporting date, invoices issued outside KSeF, and other types of evidence.

The regulation confirms that penalties for incorrectly completed JPK_VAT files are not automatic. Taxpayers retain the ability to correct errors, including those identified by the tax authorities. Importantly, the alignment applies from settlement periods starting on 1 February 2026, avoiding unnecessary fragmentation during the phased KSeF rollout.

Transitional Rules Do Not Eliminate Compliance Risk

Although transitional measures allow continued use of certain authentication methods for a limited period, these should not be mistaken for long-term solutions. The regulatory direction clearly favors standardized certificate-based access and fully integrated reporting.

Taxpayers that rely heavily on transitional mechanisms risk operational disruption once these measures expire.

Practical Implications for 2026

Taken together, the December 2025 implementing regulations indicate that KSeF has entered its final operational form. Companies should prioritize:

• Reviewing transaction types against defined scope exclusions
• Updating simplified invoice processes for KSeF issuance
• Finalizing authorization and authentication governance
• Preparing for consistent use of KSeF numbers in VAT reporting
• Testing offline and exceptional scenarios

The regulatory debate around KSeF has largely concluded. The remaining challenge is execution.

Key Compliance Questions for KSeF 2026