TL;DR
  • KSeF (Krajowy System e-Faktur) is Poland's mandatory e-invoicing system — live since Feb 1, 2026.
  • If you sell to Polish VAT-registered businesses AND you have a Polish tax ID (NIP), you MUST issue invoices through KSeF.
  • If you are a foreign seller WITHOUT a Polish NIP, KSeF is optional — but Polish buyers may ask for KSeF invoices anyway.
  • Penalties for non-compliance: up to 100% of the invoice's VAT (Polish VAT Act art. 106ni).
  • Fakturium issues fully KSeF-compliant invoices in PLN, EUR, USD and any currency at NBP exchange rates.

If you run a business outside Poland and sell to Polish companies, you've probably heard about KSeF — the Polish "Krajowy System e-Faktur" (National e-Invoice System). As of February 1, 2026, KSeF is mandatory for most VAT-registered Polish businesses. This article explains what it means for YOU as a foreign seller, what you must do, and what you can ignore.

What is KSeF exactly?

KSeF is a centralized government platform operated by the Polish Ministry of Finance. Every B2B invoice issued by a Polish VAT taxpayer must be sent to KSeF in a structured XML format (called "FA(3)"). The Ministry assigns a unique KSeF ID, and that ID — not the PDF — is what counts as legal proof the invoice was issued.

Think of it as the Polish equivalent of Italy's SDI (Sistema di Interscambio), Spain's TicketBAI, or France's upcoming PPF/PDP system. The EU's broader VAT in the Digital Age (ViDA) directive will eventually harmonize all of these, but until then each country runs its own platform.

Legal basis
Polish VAT Act, art. 106na
Defines KSeF as the authoritative system for issuing structured invoices and assigns the legal weight to the KSeF ID rather than the PDF visual.

Does KSeF apply to YOUR company?

The short answer: only if you have a Polish tax ID (NIP) AND you are a Polish VAT taxpayer. A foreign company without a Polish NIP is not subject to the KSeF mandate — even if you sell to Polish customers.

However, three scenarios change this:

  • You opened a Polish branch / "oddział" — that branch usually gets a Polish NIP and is treated as a Polish taxpayer.
  • You registered for Polish VAT under the standard procedure (not OSS/IOSS) — registration gives you a NIP, which puts you in scope.
  • You established a permanent establishment ("zakład") in Poland — typically a long-term office or production facility — which also triggers Polish tax residency.
Note

OSS (One-Stop Shop) for B2C e-commerce does NOT trigger KSeF. You report VAT through the OSS portal in your home country, and you don't need a Polish NIP. KSeF is a B2B thing.

What if a Polish customer asks for a KSeF invoice?

This happens often. A Polish buyer may insist on receiving an invoice "through KSeF" because their accounting software auto-imports invoices from the KSeF API. If you're not a Polish taxpayer, you legally don't have to comply — but you have options:

  • Send a standard PDF invoice (with your foreign tax ID + EU VAT number if you have one). For B2B intra-EU supplies, this is a "reverse charge" invoice and the Polish buyer handles VAT on their side.
  • If you want to integrate with KSeF voluntarily, you'll need to: (a) get a Polish NIP, (b) register a tax representative in Poland, (c) use a system like Fakturium that supports both PL and foreign senders.
  • Refuse — and politely explain you are not a Polish VAT taxpayer. Most accounting departments understand this.
Practical tip

If you sell regularly to Polish customers (5+ invoices/month), voluntary KSeF registration speeds up payments because invoices auto-import into Polish ERPs. Talk to your tax advisor about the ROI before committing — it's a 3-6 month setup.

Currency, exchange rates, language

Polish law requires that invoices issued by Polish taxpayers show the VAT amount in PLN, even if the invoice itself is in a foreign currency. The conversion uses the National Bank of Poland (NBP) reference rate from the day BEFORE the tax obligation date — usually the day before the supply date or the day before the invoice date, whichever comes first.

Legal basis
Polish VAT Act, art. 31a
Mandates the use of NBP average exchange rates for VAT conversion. Fakturium fetches NBP rates automatically when you select a foreign currency.

The invoice can be written in any language, but a translation into Polish must be available for tax inspection. Standard practice: bilingual invoices (English + Polish) with parallel labels. Fakturium generates these automatically for EUR/USD/GBP invoices.

Penalties for ignoring KSeF

If you're a Polish taxpayer and you fail to use KSeF when required:

  • Fine of up to 100% of the VAT amount shown on the invoice (Polish VAT Act art. 106ni).
  • If the invoice is issued outside KSeF when KSeF is mandatory, the buyer technically cannot deduct VAT — this creates customer disputes.
  • Repeated violations: criminal liability under the Polish Fiscal Penal Code (KKS) — fines and, in extreme cases, restrictions on business activity.
Warning

Foreign companies without a Polish NIP are NOT subject to these penalties. The mandate only binds Polish VAT taxpayers. Don't let aggressive accounting departments tell you otherwise.

When does Fakturium help?

Fakturium is built for Polish KSeF compliance, but it handles foreign-currency invoices for Polish exporters and for foreign founders running PL entities. Typical use cases:

  • You run a Polish sp. z o.o. (LLC) as a foreign founder and need to issue invoices in EUR/USD to international clients.
  • You're a Polish freelancer billing US/EU clients on Upwork, Toptal or directly.
  • Your Polish accountant uses iFirma, but you want an English-language UI to issue invoices yourself without bothering them every time.

Plans start at 0 zł / month (5 invoices). Pro at 99 zł / month is unlimited + NBP rates + bilingual PDFs. No credit card required to test.

Bottom line

  • No Polish NIP → KSeF doesn't apply to you. Send standard PDF invoices.
  • Polish NIP + Polish VAT taxpayer → KSeF is mandatory. Use Fakturium or another KSeF-integrated system.
  • Foreign currency invoices → NBP rate, day before tax obligation, bilingual PDF recommended.
  • Polish buyer "demanding" KSeF when you have no NIP → polite refusal is legal. Reverse-charge B2B invoice is the EU-standard answer.