KSeF Poland: 2026 National e-Invoicing System Guide for VAT Taxpayers

Starting in 2026, the National e-Invoicing System will become mandatory for most businesses in Poland – including both active VAT taxpayers and those exempts. This marks a major shift in how invoices are issued, delivered, and stored. Adapting to the new system will require not only technical adjustments but also changes in internal processes. In this article, we explain what KSeF is, how it works, who will be affected by the new regulations, and what tools and solutions are being provided to support the transition. If you want to avoid disruptions and ensure compliance, this step-by-step guide is for you.

 

KSeF – the National e-Invoice System (Krajowy System e-Faktur) is a digital platform

KSeF  enables the issuance, receipt, and storage of invoices in a structured format (so-called e-invoices or structured invoices).

These new e-invoices should not be confused with previously used invoices issued in electronic form. Within KSeF, each invoice is assigned a unique identification number to prevent loss, and the system allows for immediate receipt of invoices upon issuance. Once the platform is fully implemented, taxpayers will no longer be required to store and archive invoices themselves.
Currently, issuing invoices through KSeF is voluntary. However, this will change in 2026, when businesses will be required to comply with the new regulations.

 

How the Polish KSeF E-Invoicing System works: technical overview

A structured invoice can be issued using commercial software that, based on the technical specifications provided by the Ministry of Finance, sends the data to the KSeF 2.0 platform. A key requirement is that the taxpayer must have a valid NIP (tax identification number). After issuing the invoice, the taxpayer will receive an official acknowledgment of receipt, and KSeF will assign a unique number to the invoice. This KSeF number should not be confused with the internal invoice numbering system used by the taxpayer. In the case of split payment mechanisms, the KSeF invoice number will be a required part of the payment title.

 

The Ministry of Finance will provide the following applications to support working with KSeF:

• KSeF 2.0 Taxpayer Application, which allows taxpayers and authorized entities to use KSeF, issue and receive e-invoices, and download official acknowledgments.
• KSeF Mobile App, which allows users to issue structured invoices.
• e-Microbusiness Application, available via the e-Tax Office, which allows linking an existing account with KSeF and managing invoices.

 

Although KSeF allows attachments to e-invoices, the type and structure of data in attachments are limited and must comply with the logical structure provided by the Ministry of Finance. Attachments such as work schedules or project budgets in PDF format will need to be sent outside the KSeF system.

Correction invoices for documents issued via KSeF must also be in structured format. If an error occurs (e.g., incorrect buyer NIP), a two-step correction will be required: first issuing a correction invoice to zero, then reissuing the original invoice with corrected data.

KSeF mandatory use: who must comply and when

The implementation of the e-invoicing system will apply to all VAT taxpayers, both active and exempt. The mandatory use of e-invoices will be phased in as follows:

• From February 1, 2026 – for large taxpayers with total sales exceeding PLN 200 million (incl. VAT) in 2024,
• From April 1, 2026 – for all other taxpayers,
• From January 1, 2027 – for the smallest, “digitally excluded” taxpayers, with gross monthly sales not exceeding PLN 10,000, as well as for transactions eligible for simplified invoices.

 

Mandatory e-invoicing will not apply to:

• RR VAT invoices documenting the purchase of agricultural products from flat-rate farmers,
• invoices issued to consumers (B2C).

However, in both of the above cases, using KSeF will remain voluntary.

Support tools and transitional relief for KSeF implementation

The regulations include several facilitations for taxpayers during the transitional period. For example, until the end of 2026, no penalties will be imposed for invoicing errors made through KSeF.

From September 30, 2025, the API interface will be made openly available for testing, allowing businesses to create their own e-invoicing platforms. In November 2025, a test version of the KSeF 2.0 Taxpayer Application will be released, allowing test invoices to be issued without legal effect.

Importantly, taxpayers will be able to issue invoices outside the system in “Offline24” mode. In such cases, the invoice must be sent to KSeF no later than the next business day. The issue date will be the date specified on the invoice by the issuer, not the system. A QR code verifying authenticity will be a mandatory element of such invoices.

 

In the event of a KSeF system failure or maintenance, emergency and offline modes are foreseen. These also allow invoices to be issued outside the system. In such cases:

• a QR code must be included,
• the invoice must be sent to KSeF within 7 business days after the end of the failure (emergency mode),
• or on the next business day following the end of the unavailability period (offline mode).

To generate the required QR codes, the taxpayer will need to download a certificate from KSeF, ideally in advance. According to the Ministry of Finance, certificates will be available from November 1, 2025.

KSeF will also include technical mechanisms to detect suspicious or potentially fraudulent invoices, allowing users to report them for review.

Key considerations for using the KSeF platform

Currently, legislative work is ongoing that may modify:

• the data scope permitted in KSeF,
• technical specifications of the system,
• or even the final deadlines for mandatory implementation.

It is highly recommended to monitor updates from the Ministry of Finance regularly.

 

Frequently Asked Questions (FAQs)

When does KSeF become mandatory?
Most businesses must comply by April 1, 2026; large taxpayers by February 1, 2026.

 

What are structured e-invoices?

Invoices submitted in XML format through the Ministry of Finance’s KSeF platform.

 

Is KSeF mandatory for B2C transactions?

No, but voluntary usage is allowed.

 

What is Offline24 mode?
  A fallback mode allowing invoice issuance during system outages, with delayed submission.