What is KSeF? Poland’s e-invoicing system explained (2026)
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Last reviewed: 26 October 2026. Dates per the Polish VAT Act as amended on 5 August 2025 (Journal of Laws 2025, item 1203).
The National e-Invoicing System (KSeF) is a government platform that became mandatory in two stages: from 1 February 2026 for taxpayers whose 2024 sales (including VAT) exceeded 200 million zł, and from 1 April 2026 for all other taxpayers. Since 1 February 2026 every business has had to receive structured invoices through KSeF.
This article explains:
- what KSeF is and how it works,
- the reasons behind its introduction,
- the legal and operational impact on businesses,
- practical steps to prepare,
- how Flowtly supports KSeF compliance.
1. What Is KSeF? [Definition]
KSeF (Krajowy System e-Faktur) is an official Polish government platform designed to handle structured electronic invoices. It enables companies to:
- issue invoices in structured XML format,
- transmit them directly to clients via the government system,
- archive documents for 10 years,
- share data with the tax office in real time.
A structured invoice is a machine-readable file format based on a fixed XML schema, ensuring compatibility with accounting software and eliminating the need for manual data entry.
2. Why Was KSeF Introduced? [Purpose]
The system is being implemented by the Polish Ministry of Finance to:
- improve VAT collection and reduce fraud,
- simplify tax settlements,
- eliminate the requirement to send JPK_FA files,
- shorten VAT refund timelines (up to 40 days),
- improve transparency and security in invoice circulation.
3. Who Must Use KSeF?
KSeF is mandatory for:
- freelancers and sole proprietors,
- small and medium-sized enterprises,
- large companies and corporations,
- foreign companies with a seat or fixed establishment in Poland.
There are exemptions and a transition period. Until 31 December 2026, taxpayers whose invoiced sales do not exceed 10 000 zł gross a month may issue invoices outside KSeF, and invoices from cash registers may also be issued outside it. The obligation does not cover invoices to consumers, or taxpayers with no seat or fixed establishment in Poland; both may use KSeF voluntarily.
4. Business Implications
Mandatory use of KSeF will significantly affect how invoices are issued and processed:
- New invoice format – PDF files will be replaced by structured XML.
- System integration – your invoicing or ERP software must connect to KSeF.
- Process adjustments – internal document workflows must be updated.
- Legal risk – an invoice issued outside KSeF when it should have gone through it breaches the obligation. No penalties apply to errors made in 2026; a bill adopted by the Council of Ministers on 20 October 2026 would extend that to 31 December 2027.
5. How to Prepare Your Company [Checklist]
To ensure a smooth transition, businesses should:
- Audit current tools – check whether your invoicing system supports XML and KSeF integration.
- Train staff – especially accountants and admin personnel.
- Run early tests – check your KSeF connection in the Ministry of Finance test environment; the smallest issuers have until 1 January 2027.
6. Flowtly’s KSeF Integration
Flowtly is integrated with KSeF. This means:
- invoices can be sent and received directly within the Flowtly platform,
- documents follow Ministry of Finance requirements,
- the invoicing workflow is handled in a single, unified environment,
- no need for additional tools or third-party services.
Flowtly ensures your business transitions to KSeF with minimal disruption and full transparency.
7. Summary
Mandatory e‑invoicing via KSeF introduces significant changes for businesses, but it also offers opportunities to modernise processes and improve fiscal transparency.
Companies that act early and adopt compatible systems – such as Flowtly – will benefit from smoother operations, lower compliance risks, and better control over financial data.