KSeF — setup and implementation

What Is KSeF and How Does It Work

KSeF is a central IT platform operated by Poland's Ministry of Finance for issuing, transmitting, and archiving structured invoices in XML format (FA_VAT schema). Every invoice issued via KSeF: is validated for structural correctness and VAT compliance; receives a unique KSeF ID assigned by the Ministry's system; is stored by the Ministry of Finance for 10 years (no additional archiving required by the company); is accessible to the buyer — no need to send the invoice by email. The structured invoice replaces traditional paper and electronic (PDF) invoices. After the mandatory KSeF deadline, traditional PDF invoices will no longer be recognized by tax authorities as valid VAT documents.

KSeF Implementation Timeline — Key Dates

KSeF operated as a voluntary system from 1 January 2022. The mandatory rollout originally planned for 2024 was postponed after system errors were discovered. Current schedule (as of July 2025): 1 February 2026 — mandatory for active VAT taxpayers with annual revenue above PLN 200 million; 1 April 2026 — mandatory for all remaining active VAT taxpayers; VAT-exempt entities — no obligation (for now). Dates may change — FlexInWork monitors the schedule and notifies clients of updates.

How to Issue an Invoice via KSeF

There are three main ways to issue invoices through KSeF. First, API integration: connect your ERP/accounting system (Comarch, Symfonia, SAP, Wapro, or similar) to the KSeF API — invoices are sent automatically without manual intervention. Second, Ministry's web portal (e-mikrofirma.mf.gov.pl): issue invoices manually directly in the KSeF system — suitable for companies issuing few invoices per month. Third, Ministry's mobile app (e-mikrofirma): for micro-businesses issuing up to a few dozen invoices monthly. Regardless of method, you need: a qualified electronic signature or trusted profile (ePUAP) for authentication; KSeF access tokens configured for individuals or systems authorized to issue invoices on behalf of the company; pre-launch testing on the Ministry's sandbox environment (demo.ksef.gov.pl).

Which Invoices Must Go Through KSeF

KSeF applies to VAT invoices issued by active Polish VAT taxpayers for: other VAT taxpayers (B2B); individual non-taxable persons (B2C) — except sales registered on a cash register and transport tickets. Invoices currently excluded from KSeF (as of 2026): invoices under debt assignment contracts; invoices issued by non-residents (foreign entities not registered for VAT in Poland); invoices for intra-community transactions (ICS/ICA) — governed by EU rules.

Penalties for Non-Compliance

After the mandatory KSeF date, a taxpayer that issues an invoice outside the system (e.g., as a PDF when KSeF was required) faces a fine of up to 100% of the VAT shown on the invoice (minimum 5%). A buyer who deducts VAT from an invoice issued outside KSeF (when the issuer was obligated to use it) loses the right to deduct that VAT. Verifying KSeF status of received invoices will therefore become a standard internal control procedure.

KSeF for Foreign-Owned Companies in Poland

Foreign-managed companies face specific KSeF challenges. Authentication in KSeF requires a qualified electronic signature or trusted profile. For foreigners without a Polish PESEL, a trusted profile is unavailable — a qualified electronic signature from an EU-notified provider is required, or the company must authorize an accounting firm. FlexInWork holds the necessary credentials and can act as an authorized KSeF invoice issuer on the client's behalf. Additionally, transitioning to KSeF requires updating or replacing the invoicing system — FlexInWork advises on selecting and configuring KSeF-compatible accounting tools.