What is KSeF? KSeF is a centralised government platform administered by Poland’s National Revenue Administration (KAS) through which all structured e-invoices must be issued and received. Invoices submitted through KSeF are stored in XML format and assigned a unique KSeF identification number, which serves as proof of acceptance into the system.
The Rollout: Who Is Affected and When
The mandatory rollout of KSeF has been phased across 2026 and 2027. The key milestones are as follows:
A critical point to note: 2026 is a transition period. During this year, no penalties are imposed for errors related to KSeF compliance, giving businesses and accounting systems the time they need to adapt. This grace period does not last forever. Sanctions will apply from 2027, including fines of up to 100% of the VAT shown on an invoice not issued through KSeF when required, and potential denial of input VAT deduction for buyers.
Note that a separate penalty of PLN 500 per error applies to incorrectly marked invoices in JPK_VAT filings — this is not covered by the 2026 waiver and applies from 25 March 2026.
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Who Must Use KSeF?
Not all entities operating in Poland fall within the mandatory scope. The obligation applies specifically to entities with an established connection to Polish VAT, and the distinction matters particularly for foreign businesses operating across borders.
A key nuance for multinational groups: a foreign entity with a fixed establishment in Poland is only obligated if that establishment directly participates in the transaction documented by the invoice. Where the Polish establishment is not part of the supply chain for a given transaction, the KSeF obligation does not apply to it, though that entity may still voluntarily choose to use the system.
Important for foreign buyers: Foreign recipients without a Polish VAT number cannot log into KSeF to access invoices. Where a seller issues a KSeF invoice to a foreign buyer, they must additionally deliver that invoice through an agreed external channel, as a PDF, by email, or on paper, accompanied by a QR code referencing the KSeF number for verification.
How Invoices Are Issued in KSeF
There are two primary modes for issuing invoices under KSeF, and understanding the distinction is critical for accounting systems and AP workflows.
Online Mode
In online mode, invoices are transmitted directly to the KSeF platform at the moment of issue. The invoice is considered officially issued once the KSeF number has been assigned by the system. Accounting systems must therefore be configured to capture the KSeF number and link it to the corresponding sales record before booking the transaction.
Offline24 Mode
In offline24 mode, the taxpayer prepares the invoice offline and submits it to KSeF within 24 hours. The crucial difference here is the issue date: it is the date entered in the P_1 field of the invoice itself, not the date of KSeF submission. The P_1 field is a mandatory data field in the Polish invoice XML schema where the taxpayer records the official date of issue. This date governs the accounting period, so accounting systems must use it correctly to avoid errors in VAT filings.
What Types of Documents Are and Are Not Issued in KSeF
KSeF applies to structured B2B invoices under Polish VAT law. Several common document types sit outside its scope, which has practical implications for AP and T&E teams:
- Proforma invoices Not VAT invoices under Polish law and never issued through KSeF. They continue to be issued freely outside the system.
- Simplified invoices Fiscal receipts that include the buyer’s VAT number, for transactions up to PLN 450 (approximately €105), remain valid outside KSeF until 30 September 2026. After that date, they must also flow through KSeF.
- Online cash register invoices (B2B) May be issued outside KSeF until end of 2026. From 1 January 2027, they must be issued in KSeF.
- Purchases from foreign suppliers Including intra-Community acquisitions and import of services, these are documented outside KSeF. The system is designed for Polish-issued invoices, not foreign purchase records.
Note: From 1 February 2026, it is possible to attach files to KSeF invoices. However, only structured XML files are accepted inside the system. PDFs, Word documents, images, and other unstructured formats cannot be attached within KSeF and may only be sent to the counterparty through external channels.
JPK_VAT Codes: BFK, DI and OFF
JPK_VAT (Jednolity Plik Kontrolny) is Poland’s Standard Audit File for Tax, the structured digital report that VAT-registered taxpayers submit monthly to thePolish tax authority. It includes both the VAT ledger and invoice-level transaction data. When invoices have not been processed through the standard KSeF online flow, three special markers are used to flag them in the JPK_VAT report:
| Marker | Name | When it applies | Key action required |
|---|---|---|---|
| BFK | No KSeF invoice | Invoices issued outside KSeF: from foreign contractors, before the mandatory date, by taxpayers not yet in scope, or related to WNT, import of services, and reverse-charge supplies | No correction needed. BFK marks that KSeF does not apply or was not available for that document |
| OFF | Offline — total system failure | Invoices issued during a total KSeF platform outage (Article 106nf). Rare in practice — applies only when the entire national system is unavailable | No correction needed. Mark applied at time of issue during outage |
| DI | Other document | Offline24 invoices or invoices from a KSeF unavailability period that do not yet have a KSeF number at the time of JPK submission. Also used for internal vouchers, WNT entries, and reverse-charge supplies | No automatic correction required. However, if a sales invoice issued in offline24 mode later receives a KSeF number after your JPK_VAT has been filed, a correction of the sales record is recommended. Purchase records do not need updating. |
Practical Obligations: What Your Business Must Do
Compliance with KSeF is not only a legal matter. It requires coordinated action across IT, finance, AP, and tax functions. The following areas require attention:
ERP and System Integration
Your accounting or ERP system must be able to connect to the KSeF platform via the official government API, generate invoices in the FA(3) XML schema (which replaced FA(2) from 1 February 2026), receive and store the KSeF number for each invoice, and handle the correct issue date in offline scenarios.
Authorisation and Access
Entities must register authorised users in KSeF via the e-Urząd Skarbowy portal. Three types of authorisation are supported: qualified electronic signature, trusted profile (Profil Zaufany), and KAS-issued certificates. Internal roles of issuer, recipient, and administrator should be defined and assigned.
Buyer Notification
Domestic Polish buyers with a VAT number can access invoices directly in KSeF. Foreign buyers and consumers must receive the invoice through an agreed external channel — PDF, email, or paper — with a QR code for verification.
Post-2026 Penalty Readiness
The 2026 transition period means no penalties are imposed this year. From 2027, sanctions include fines of up to 100% of the VAT on a non-compliant invoice, and denial of input VAT deduction for buyers who failed to verify KSeF compliance.
What This Means for VAT Recovery
KSeF is not only a compliance reform. It also creates real opportunities to improve VAT recovery outcomes for businesses operating in Poland.
The 10-year automatic archiving of structured invoices means that the documentation trail required for VAT reclaim is preserved by default. At the same time, the mandatory structured XML format makes invoices fully machine-readable, enabling faster and more accurate extraction of the data needed for VAT calculations and claim preparation.
For businesses with significant Polish AP or T&E spend, the combination of structured invoice data and automated VAT rules processing creates a stronger foundation for maximising recoverable VAT, provided the right processes and systems are in place upstream.
VAT4U and KSeF: VAT4U’s Comply module supports automated Polish KSeF verification, validating that invoices carry a valid KSeF number and flagging those that should have been issued through the system but were not. For AP teams processing high volumes of Polish invoices, this means compliance checks happen automatically, without manual review. VAT4U introduced this capability directly into the invoice validation workflow in April 2026.
Key Benefits KSeF Delivers
- Shorter VAT refund period: reduced from 60 to 40 days for taxpayers using KSeF
- Elimination of paper and email-based B2B invoice exchange in domestic transactions
- Reduced invoice fraud risk: every invoice carries a verifiable KSeF number
- 10-year automatic archiving: invoices stored in KSeF from the end of the year of issue
- Simplified VAT reconciliation: KSeF data can be cross-referenced with JPK_VAT automatically
- Real-time access to issued and received invoices for both sellers and buyers
What to Act on Now
Poland’s KSeF mandate represents a structural change to how invoices are created, transmitted, and used as VAT evidence. For most Polish VAT-registered businesses, the obligation has been in force since 1 April 2026. While 2026 carries no penalties for KSeF invoicing errors, organisations that delay system and process adaptation are building risk for 2027.
The practical priorities are clear: confirm whether your entity falls within scope, check that your ERP or accounting system can connect to the KSeF platform and handle both online and offline24 modes, establish the right access roles in the portal, and review your document delivery process for foreign buyers who cannot access KSeF directly.
If your AP or T&E operations include significant Polish spend, this is also a moment to review whether your VAT recovery process can take advantage of the structured, machine-readable invoice data that KSeF now provides at scale.
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REQUEST A DEMOFAQ about KSeF
KSeF stands for Krajowy System e-Faktur, which translates as the National e-Invoice System. It is a centralised platform operated by Poland’s National Revenue Administration (KAS) through which VAT-registered businesses must issue and receive structured electronic invoices. All invoices in KSeF are stored in XML format and assigned a unique identifying number as proof of acceptance.
Yes. KSeF became mandatory for large taxpayers (with VAT turnover above PLN 200 million in 2024) on 1 February 2026, and for all remaining Polish VAT-registered taxpayers on 1 April 2026. However, 2026 is a transition period: no penalties are imposed for KSeF errors during this year, giving businesses time to adapt their systems.
Foreign entities without a place of business or fixed establishment in Poland are not subject to the KSeF obligation. A foreign entity that has a fixed establishment in Poland is only obligated if that establishment directly participates in the transaction being invoiced. Foreign companies may also voluntarily join KSeF even if they are not required to do so.
Foreign buyers without a Polish VAT number cannot access KSeF directly. When a seller issues a KSeF invoice to a foreign buyer, they must also deliver it through an agreed external channel, such as PDF, email, or paper. The invoice includes a QR code that references the KSeF number, allowing the buyer to verify its authenticity.
In online mode, the invoice is sent directly to KSeF at the moment of issue and is considered issued once the system assigns a KSeF number. In offline24 mode, the taxpayer prepares the invoice offline and has up to 24 hours to submit it to KSeF. The official date of issue is the date recorded in the P_1 field of the invoice, not the submission date. This distinction determines the correct accounting period.
No. A proforma invoice is not a VAT invoice under Polish law and is therefore not issued through KSeF. Proforma documents continue to be issued freely outside the system.
During 2026, penalties for failing to issue invoices through KSeF are waived. However, a separate PLN 500 per-error fine applies to incorrectly marked invoices in JPK_VAT filings and is enforceable from 25 March 2026. From 2027, full sanctions apply including fines of up to 100% of the VAT amount and denial of input VAT deduction. After the transition period ends, sanctions include a fine of up to 100% of the VAT amount shown on an invoice that was not issued through KSeF when required. Buyers may also be denied the right to deduct input VAT on invoices received outside KSeF when they should have verified KSeF compliance.
KSeF creates a stronger foundation for VAT recovery. Invoices are automatically archived for 10 years in a structured, machine-readable format, which simplifies documentation retrieval for VAT claims. For AP and T&E teams, the key requirement is ensuring that invoices entering your systems are KSeF-compliant, meaning they carry a valid KSeF number. Tools like VAT4U automate this validation so that non-compliant invoices are flagged before they cause issues at the claim stage.
