E-invoicing in Poland. Quick guide

Poland is gradually transitioning to a mandatory e-invoicing regime centred on the National e-Invoicing System (Krajowy System e-Faktur – KSeF). The reform will fundamentally change how businesses create, submit, receive, and archive invoices. Below you will find an updated guide including latest clarifications.

What is KSeF?

KSeF is a state-run system intended for issuing, transmitting, receiving, and retaining structured invoices in XML format. From 1 February 2026 onward, it will gradually encompass all taxpayers in Poland.

To use KSeF, taxpayers may rely on: integrated accounting or ERP systems (via API), the free KSeF Taxpayer Application (online), or the KSeF Mobile App (smartphone). There is also a possibility to use the e-Tax Office (e-US) account, linked to KSeF, to issue and receive invoices and automatically transfer them to VAT registers.

An e-Invoice is a compliant XML file submitted into KSeF, assigned a unique KSeF number. It is then stored in the system for 10 years (removing the risk of loss or destruction).

Timeline

The mandatory deployment of KSeF is scheduled in two phases. Beginning on 1 February 2026, entities whose total turnover (including VAT) in 2024 exceeded PLN 200 million will be required to issue invoices exclusively through KSeF.

On 1 April 2026, the obligation will extend to all other VAT-registered entities.

Until 31 December 2026, there is a transitional rule allowing issuance of invoices outside KSeF (paper or non-structured electronic) in a given month if the total value (including VAT) of those invoices does not exceed PLN 10,000. This concession aims to ease the transition for smaller taxpayers.

The two-phase rollout (February and April) was adopted following recommendations from an IT audit and in response to concerns from smaller enterprises needing extra preparation time.

Benefits

KSeF brings several tangible advantages: faster VAT refunds (reduced from 60 to 40 days), a unified invoicing process with lower risk of mistakes, real-time invoice delivery to recipients, and automatic archiving (for 10 years) without need for manual storage.

It also strengthens trust among parties — the buyer knows the invoice was legally issued.

Challenges & Clarifications

One challenge is connectivity: internet access is necessary to issue invoices via KSeF. For entrepreneurs without internet or computer use, they must delegate invoice issuance (e.g., to an accounting firm) via proper authorizations.

Another important element is the concept of offline modes (offline24, offline during system unavailability, or emergency mode). These allow issuing invoices temporarily outside KSeF, with the requirement to submit them into KSeF later (within specified timeframes). For offline24 mode, submission must occur no later than the next business day. These invoices must carry two QR codes (one of which is generated using a KSeF certificate).

In the online mode, the invoice must be sent to KSeF on the same day as its issuance. If submission occurs later, the system treats it as offline24 issuance. If the system assigns the KSeF number only the following day, the invoice date remains the date of submission to KSeF (not the numbering date).

Once an invoice is accepted into KSeF, it becomes a legal document that cannot be edited. In case of a mistake, one issues a corrective invoice (credit note). If an XML file is rejected (due to format errors or missing elements), the invoice is not considered issued — you must send a correct version.

KSeF does not validate correctness of contractor data (e.g. NIP). If an incorrect NIP is inserted, the system accepts it; later correction must happen via a zero-amount correction and reissuance to the proper NIP.

In terms of document scope, KSeF covers only invoices — not purchase orders or delivery notes. Proforma documents are not treated as invoices and are excluded.

Invoices to consumers (B2C) remain voluntary in KSeF — even after the mandatory dates.

Regarding international and cross-border relations: foreign suppliers are not required to report invoices into KSeF (the system targets Polish VAT invoicing). However, foreign entities with a Polish VAT registration may voluntarily use KSeF.

For invoices issued to foreign clients, the seller may issue via KSeF, but must also deliver the invoice outside KSeF (e.g. PDF or email) — the invoice must include a QR code for verification.

About attachments: starting 1 February 2026, KSeF will allow structured XML attachments (not PDFs or images). But attachments are optional. To issue invoices with attachments, the taxpayer must submit a notification in the e-Tax Office (e-US) from 1 January 2026. The notification is processed within up to 3 business days. Attachments can be accepted only by accounting software integrated via API — the free MF tool provided by the State will not support attachments.

Invoices with attachments must not exceed 3 MB. Non-invoice documents (e.g. waybills, acceptance protocols) cannot be included as attachments in KSeF — they must be transmitted outside the system.

KSeF will adopt a new invoice structure, FA(3), starting 1 February 2026.

This new structure adds improvements: support for attachments, expanded description fields, changes aiding local government units (JST / GV), and better handling of payment due dates.

There is also a planned requirement (effective 1 January 2027) that the KSeF number must be included in payment references (for payments tied to split payment mechanism). This is to counter late payments and improve clarity in payment matching.

Practical steps to prepare

Check whether your ERP or accounting software supports KSeF integration via API and the new FA(3) structure. Begin voluntary issuance ahead of 2026 to test workflows and avoid surprises. Adapt your internal invoice approval, archiving, and error-handling procedures to reflect the non-editability of invoices in KSeF. Prepare staff to understand online vs offline modes, QR code requirements, and corrective invoice processes. If your business may need to issue invoices with attachments, plan to submit the appropriate notification in e-US starting January 2026 and ensure your software supports attachments via API.

Ensure that even before your mandatory start date, you are ready to receive invoices through KSeF (this obligation applies from 1 February 2026 for all). Monitor whether new invoices for your company arrive in KSeF — the system itself does not send notifications; your software should poll for new invoices or use API to fetch them.

If you commit to using offline modes (offline24 or during outages), you must comply with the timelines and QR coding rules. Factor this into your internal procedures.

Lastly, since invoices in KSeF cannot be modified once accepted, you must design your validation checks carefully before submission and set up a proper corrective invoice (or zero correction + reissue) policy.