The introduction of mandatory e-invoicing through Poland’s National e-Invoicing System (KSeF) is one of the most significant changes to the Polish tax system in recent years. From 2026, most VAT taxpayers will be required to issue structured invoices in a unified format and submit them to a central system acting as a repository of sales documents.

This change affects not only the technical process of issuing invoices but also the moment of issuance, delivery and recognition for tax purposes.

Implementation timeline

The obligation to use KSeF will be introduced in stages. From 1 February 2026 it will apply to the largest taxpayers (with revenue above PLN 200 million), and from 1 April 2026 to the remaining VAT taxpayers.

A transitional period until the end of 2026 is provided for the smallest entities, whose monthly sales do not exceed PLN 10,000 or who document sales exclusively using cash registers or simplified invoices. They will be required to use KSeF from 1 January 2027, although they may opt in earlier voluntarily.

When invoices are not subject to KSeF

Certain transactions remain outside the scope of mandatory KSeF, including B2C transactions, selected international procedures (OSS/IOSS), specific transport services documented with tickets and some self-billing cases without a Polish VAT number.

Invoice issuance modes

The system allows three issuance modes: real-time online, offline24 (with submission to KSeF no later than the next business day) and an emergency mode used when the system is unavailable.

Foreign currency invoices

KSeF allows invoices to be issued in foreign currencies. Net and gross values may be expressed in the foreign currency, but VAT must always be reported in PLN. The exchange rate is generally based on the average NBP rate from the day preceding the invoice issue date. The offline24 mode ensures consistency between the issue date and the applied exchange rate, even if the invoice is uploaded later.

Advance invoices in KSeF

When payment is received before the supply of goods or services, an advance invoice must be issued in KSeF. The FA(3) structure introduces clear labels distinguishing advance, final and corrective invoices.

Advance invoices should include details of the underlying order or contract. If advance payments do not cover the full price, a final invoice must be issued after delivery, reduced by the advances received. If advances cover 100% of the price, the last advance invoice functions as the final invoice.

Corrective invoices

Once an invoice receives a KSeF number, it cannot be cancelled. Any errors must be corrected by issuing a corrective invoice within the system. Buyer-issued correction notes will no longer be allowed.

The scope of required data remains consistent with VAT regulations, including the obligation to indicate corrected tax bases and VAT amounts or the correct content of amended fields.

Special attention should be paid to incorrect VAT identification numbers – in such cases the original invoice must be corrected to zero and reissued correctly.

Conclusion

The implementation of KSeF represents a fundamental shift in invoicing processes in Poland. Businesses should prepare not only their IT systems but also internal procedures and workflows.

Proper preparation – especially in the areas of foreign currency invoices, advance payments and corrections – will help minimize risks, ensure compliance and streamline accounting processes.