The costliest mistakes Ukrainian business owners make in Poland do not come from ignorance of the law. They come from words that look alike. A Polish faktura sounds like a Ukrainian податкова накладна, KSeF looks like ЄРПН, and mObywatel reads as the Polish Diia. Behind each resemblance sits a different legal mechanism.
This stopped being a convenience question. KSeF (Krajowy System e-Faktur, Poland's national e-invoicing system) has been mandatory since 1 February 2026 for the largest taxpayers and since 1 April 2026 for the remaining VAT payers. The window for issuing small invoices outside the system closes on 31 December 2026, and administrative penalties start on 1 January 2027.
Below is the parallel glossary: what maps onto what, and where the analogy breaks.
Legal form: FOP does not translate cleanly into JDG
The closest Polish equivalent of ФОП is JDG (jednoosobowa działalność gospodarcza, sole proprietorship) registered in CEIDG, the national business register. The similarity ends at the definition.
Ukraine Poland Where the analogy breaks ФОП JDG in CEIDG no "groups", the choice is about the taxation method single tax groups 1, 2, 3 skala podatkowa (progressive), podatek liniowy (flat), ryczałt (lump-sum on revenue) ryczałt is not "group 3": the rate depends on the type of service, not on a status ТОВ spółka z o.o. (limited company) in the KRS register different capital rules and different partner liability
Registration rules for Ukrainian citizens changed on 5 March 2026. Holders of a PESEL number with UKR status who are temporary protection beneficiaries may run a business on the same terms as Polish citizens, and businesses registered before that date may continue for the duration of legal residence. Current conditions are published on biznes.gov.pl.
The practical takeaway: in Poland your residence title decides whether you may run a business, not the mere fact of holding a PESEL number.
Identifiers: one Ukrainian number, three Polish ones
In Ukraine an individual operates under a single tax number, a company under ЄДРПОУ. Poland splits this into three identifiers with distinct jobs.
PESEL identifies a person, not a business. It is the precondition for a Profil Zaufany.
NIP identifies a taxpayer. For a JDG it is the company number and, at the same time, the operating context inside KSeF.
REGON is a statistical number, rarely used in day-to-day trade.
Inside KSeF, NIP is what counts. It sets the authentication context, meaning whose invoices you are allowed to issue and download.
Digital identity: Diia is not Profil Zaufany
This is the most common misunderstanding and the most expensive one in lost time.
Ukraine Poland Note Diia app mObywatel functionally similar, legally separate systems Дія.Підпис (Ukrainian qualified signature) podpis kwalifikowany (EU qualified signature) in the EU the Ukrainian signature ranks as advanced, not qualified login via Diia Profil Zaufany, e-dowód, online banking, mObywatel through Węzeł krajowy requires a Polish digital identity
Profil Zaufany, a free government eID and e-signature, is available to any individual holding a PESEL number, foreigners included. Confirmation runs through Polish online banking, an in-person confirmation point, or a video call with an official, as described on gov.pl/web/profilzaufany.
Дія.Підпис-EU passed European technical validation and can be used to sign contracts with EU counterparties. But according to the Ukrainian government's announcement this is about member states being able to verify the signature, not about logging into Polish administration systems. It will not get you into KSeF.
There is a route for people without a PESEL. A qualified electronic signature that carries neither NIP nor PESEL is registered in KSeF through the ZAW-FA notification as so-called unique data, the fingerprint of the signing certificate. The procedure, including a worked example of a French accountant acting for a Polish-registered company, is covered in the KSeF 2.0 Handbook, part I.
Invoice vs tax invoice: false friend number one
Ukraine runs two separate documents: рахунок-фактура, the commercial invoice, and податкова накладна, the tax invoice registered in ЄРПН. An акт виконаних робіт, a service acceptance act, usually accompanies them.
Poland has one document. A faktura VAT is the commercial and the tax document at once. There is no separate tax invoice to register, and no mandatory acceptance act as a condition of booking the transaction.
The consequence is direct: a Polish buyer deducts VAT from the invoice itself. Errors are fixed with a faktura korygująca, a correction invoice, not with a correction calculation attached to a second document.
KSeF vs ЄРПН: similar mechanics, different object
Here the analogy is tempting and partly right. Both are central state registries, both assign a number to the document, and both return a receipt.
ЄРПН KSeF registers the tax invoice, the commercial document stays outside registers the invoice itself, which becomes a structured invoice квитанція, registration receipt UPO, official confirmation of receipt tax invoice registration number KSeF number, mandatory in bank transfer references from 1 January 2027 XML format set by the tax service FA(3) schema, mandatory from 1 February 2026
The detail that surprises newcomers most: in Poland you push invoices into KSeF even when you are VAT-exempt. The obligation covers VAT taxpayers, including those exempt by turnover, not only active ones. Scope and timing are published on ksef.podatki.gov.pl.
Until 31 December 2026 a deferral applies to small sales: B2B invoices up to PLN 10,000 gross per month may still be issued outside KSeF. Crossing that threshold once ends the deferral permanently. Only sales subject to the KSeF obligation count toward it, consumer sales do not.
Taxes and contributions, translated
Ukraine Poland Comment ЄСВ, unified social contribution ZUS contributions multi-component in Poland, tied to how long the business has existed rather than to the minimum wage VAT registration threshold held for years at UAH 1 million VAT exemption up to PLN 240,000 net per year raised from PLN 200,000 on 1 January 2026 (art. 113 sec. 1 of the Polish VAT Act) Electronic taxpayer cabinet e-Urząd Skarbowy login via Profil Zaufany, mObywatel, e-dowód or banking ПРРО, software cash register online fiscal cash register required only in some industries and for consumer sales
First-week checklist
Confirm that your residence title permits business activity before you file the CEIDG-1 application.
Set up a Profil Zaufany and confirm it through a Polish bank or a confirmation point.
Decide whether you stay VAT-exempt up to PLN 240,000 or register as an active VAT payer.
Open the KSeF Taxpayer Application, review your permissions and generate a KSeF certificate.
Without a PESEL, prepare a ZAW-FA with the unique data of your qualified signature.
Add up this month's B2B sales and check them against the PLN 10,000 gross threshold.
Choose invoicing software that handles FA(3), KSeF certificates and inbound invoice import.
Summary
The resemblance between the two vocabularies is a trap, not a shortcut. FOP is not JDG, ЄРПН is not KSeF, and Diia will not open a Polish office door. Once these concepts sit in the right place, the rest is tool configuration.
Biurko is a Polish invoicing and KSeF platform with a Ukrainian-language interface, KSeF certificate authentication, FA(3) support, inbound invoice import and plain-language translation of KSeF errors. You can open a free account at biurko.io with no card and no time limit.
FAQ
Can a Ukrainian citizen register a JDG in Poland? Yes, with a PESEL number and a residence title that permits business activity. Holders of PESEL UKR under temporary protection operate on the same terms as Polish citizens. Current conditions are published on biznes.gov.pl.
Does Дія.Підпис work with KSeF? No. In the EU the Ukrainian qualified signature is treated as an advanced signature and is not used to log into Polish administration systems. KSeF accepts Profil Zaufany, a qualified signature, a qualified seal or a KSeF certificate.
Do I need to issue a tax invoice separately in Poland? No. The Polish faktura VAT is the commercial and the tax document in one. There is no second document and no separate registration, but there is an obligation to send the invoice to KSeF.
What is the Polish equivalent of the Ukrainian registration receipt? UPO, the official confirmation of receipt issued by KSeF. It carries the KSeF number assigned to the invoice and proves the system accepted the document.
Does a VAT-exempt business have to use KSeF? Yes. The obligation covers VAT taxpayers, including those exempt by turnover. Until 31 December 2026 the deferral for B2B sales up to PLN 10,000 gross per month applies, but a single breach ends it permanently.