KSeF explained for foreigners running a JDG

If you run a one-person business in Poland (a JDG, or jednoosobowa działalność gospodarcza), you probably know the word KSeF. Your accountant, a client, or a forum thread can be the source. This guide explains KSeF in plain English. It explains what KSeF is, why it exists, and what it changes for you every day.

This is general information, not tax advice. If the treatment depends on your situation, ask your accountant.

What KSeF is

KSeF means Krajowy System e-Faktur, the National e-Invoicing System. It is a central system of the Polish Ministry of Finance. Before KSeF, you emailed a PDF to your client and kept a copy. Now you create a structured invoice (an XML file) and send it to KSeF. KSeF checks the invoice and stores it. It gives the invoice a unique KSeF number.

The structured format is FA(3). The PDF that you know is now only a readable view of the data. The invoice is the XML file that KSeF holds.

When KSeF accepts your invoice, it also gives you an official confirmation of receipt. This is the UPO (Urzędowe Poświadczenie Odbioru). Keep it. It proves when you submitted the invoice.

Why it exists

The tax authority wants to see invoices when they are issued, in a standard format. For the state, this makes VAT checks easier. For businesses, it means less manual data entry. A purchase invoice arrives as data. You do not retype it from a PDF.

Who has to use it

In short, almost every VAT-registered business must use it. Many other businesses that issue invoices to other businesses in Poland must also use it. The start was in phases:

• From 1 February 2026, all taxpayers receive invoices through KSeF.
• Issuing invoices through KSeF became mandatory from 1 February 2026 for the largest firms. It became mandatory from 1 April 2026 for all other taxpayers.
• A transition applies for very small volumes. If your invoices total no more than 10,000 PLN gross in a month, you can issue outside KSeF until 31 December 2026.
• Penalties for breaking the rules start on 1 January 2027.

For details, see the separate guide on KSeF deadlines. Your numbers decide if the small-volume rule applies to you. Ask your accountant to confirm.

Why foreigners are affected too

KSeF does not check your passport. It checks if you are an entrepreneur registered in Poland. If you run a JDG and invoice Polish companies, KSeF applies to you in the same way as to a Polish citizen.

Foreign clients are different. Many foreign clients do not use KSeF, so they cannot receive an invoice there. In practice, you still send them a copy by email, usually a PDF. The case decides if and how an invoice to a foreign client goes through KSeF. Ask your accountant. See our guide on invoicing foreign clients.

The English problem

The official KSeF tools and most of the documentation are in Polish. Many people who run a JDG in Poland do not speak Polish well. Their accountant can be the only person who understands the system. Fiskora aims to fill this gap. It is invoicing software in English. It makes a Polish-and-English PDF, so that you and your client can read the invoice.

How you actually get access

KSeF must know that the person who sends an invoice is allowed to act for your company. The current method uses a KSeF certificate. You generate the certificate yourself in the official KSeF application for taxpayers (Aplikacja Podatnika KSeF). You log in to it with one of these methods: Profil Zaufany, a bank login, an e-dowód (the Polish electronic ID card) or a qualified electronic signature.

The certificate is a file plus a password. You give the file to your invoicing software. The software then sends invoices for you. Our separate guide explains this at a high level. The official screens change from time to time. Follow what the KSeF app shows.

What changes in your daily routine

If you use software made for KSeF, the changes are small compared with a PDF in a word processor:

1. Enter the client, items, currency and dates as before.
2. The software builds the FA(3) invoice and sends it to KSeF.
3. KSeF returns the KSeF number and the UPO.
4. Email the PDF to your client, because most clients still expect one.
5. KSeF shows the invoices that your suppliers issue to you. The software pulls them in for you and your accountant.

Corrections also work differently. You do not edit an invoice that is in KSeF. You issue a correction invoice that refers to the original invoice.

Your accountant

Your accountant probably knows KSeF already. Your accountant can ask for access to your invoices. A good setup lets your accountant see and export issued and received invoices. Then you do not forward files. Fiskora includes a free read-only login for your accountant, with exports.

Where Fiskora fits

Fiskora is invoicing software for sole traders in Poland. With Fiskora, you can do these tasks:

• issue FA(3) invoices and send them to KSeF with the UPO;
• receive purchase invoices from KSeF;
• email PDFs to clients;
• issue corrections;
• invoice in other currencies with the NBP rate applied;
• produce bilingual Polish/English PDFs;
• handle reverse charge and services to foreign clients;
• look up VIES and the MF VAT whitelist.

Fiskora is not bookkeeping software and does not file taxes. You still need an accountant or a separate tool for that.

A simple checklist

• Ask your accountant if you must issue invoices in KSeF now, or if you can use the 10,000 PLN monthly transition until the end of 2026.
• Decide how you log in to the KSeF app (Profil Zaufany, bank, e-dowód or qualified signature).
• Generate a KSeF certificate. Store the file and password safely.
• Connect your invoicing software and test it.
• Tell your accountant how they access your invoices.

Start early. The first connection is the slowest part. The date 1 January 2027 is closer than it looks.