What is KSeF in Poland, and what does it change for a small business?

KSeF (Krajowy System e-Faktur, the National e-Invoicing System) is the Ministry of Finance’s system for issuing and receiving invoices as structured electronic files. Every business has had to receive invoices through it since 1 February 2026. Almost every business has had to issue its invoices to other businesses there since 1 April 2026.

Small issuers have a relief until 31 December 2026, and penalties are in the law from 1 January 2027. KSeF changes where your invoices are made and kept. It does not change how much VAT or income tax you pay.

What a KSeF invoice is, and what the KSeF number means

An invoice in KSeF is not a PDF. It is a structured XML file in the official FA(3) format. You send it to the Ministry’s system, which checks it and gives it a unique KSeF number (numer KSeF). KSeF keeps it for 10 years, and the buyer sees it in their own KSeF account. A PDF with a QR code is only a picture of that file.

In practice:

• Your buyer does not accept anything. An invoice counts as received on the date KSeF assigns its number.
• KSeF sends no notifications. You, your software or your accountant must look for new invoices.
• Your NIP is the address. Since 1 February 2026 a business buyer, VAT-exempt ones included, must give the seller its NIP (tax number) when it buys for the business. An invoice without your NIP lands nowhere you can see.
• Mistakes are corrected, never edited. An accepted invoice cannot be changed or cancelled; you issue a corrective invoice. KSeF checks the format and your permissions, not your arithmetic.

The KSeF number also appears in two other places:

• In your VAT file. Since February 2026, active VAT payers quote it on each invoice line of their electronic VAT file (JPK_V7M, or JPK_V7K for quarterly filers). An invoice issued outside KSeF gets a marker such as BFK instead.
• In bank transfers. From 1 January 2027, when one active VAT payer pays another for a KSeF invoice by bank transfer, the transfer must quote the number. So must a split payment message (mechanizm podzielonej płatności, the VAT part paid to a separate account).

Who must use KSeF, and from when

The 10,000 PLN relief in 2026 is narrow

• It is gross (VAT included) and counted by issue date: an invoice for an April job issued on 7 May counts in May.
• It counts only invoices that must go through KSeF. Invoices to private individuals, invoices from a cash register and receipts with a NIP are left out. Invoices to foreign business clients are issued in KSeF, so they count.
• It is lost from the invoice that takes the month over 10,000 PLN, and it does not come back: you stay in KSeF for good, even if later months are lower.

Example: In November 2026 you invoice a Polish client 7,380 PLN gross (6,000 PLN plus 23% VAT) on the 3rd, then 3,690 PLN gross on the 20th. The month reaches 11,070 PLN. The first invoice could be a PDF; the second must be issued in KSeF, and so must every invoice after it.

Receiving has no relief: the invoices your Polish suppliers issue to you are already in KSeF.

Does KSeF apply if you are VAT-exempt, on ryczałt, or a company?

VAT-exempt: yes. The Ministry’s rule is that every taxpayer, active or exempt, that has to issue an invoice issues it in KSeF. An exempt business issues invoices only when a buyer asks, or when the law requires one (for example, for services to a foreign business). When that invoice goes to a business, it goes through KSeF, on the same dates and with the same 10,000 PLN relief.

Staying under the 240,000 PLN VAT exemption limit changes your VAT, not your KSeF duties.

Ryczałt: yes. KSeF is part of the VAT rules. Your income-tax form plays no part: ryczałt (the lump-sum tax on revenue), the tax scale and flat tax are all treated the same.

Selling only to private individuals: optional. Invoices to consumers are voluntary in KSeF, in 2026 and after. If you do issue one in KSeF, give the customer a printout or PDF with its QR code.

A sp. z o.o. (limited liability company): yes, on the same dates. Only the login differs (below).

How to log in, and how to give your accountant access

You need no paid software. The Ministry offers three free tools:

• Aplikacja Podatnika KSeF 2.0 (the Taxpayer’s App), a web app at ap.ksef.mf.gov.pl: issue, receive, search and download invoices as XML or PDF, and manage permissions.
• The KSeF mobile app (Aplikacja Mobilna KSeF).
• e-mikrofirma in e-Urząd Skarbowy (the online tax office), which also moves invoices straight into your VAT records.

A sole trader logs in:

• through login.gov.pl, the national login gateway (open for KSeF since 14 February 2026), with the mObywatel app (the government’s ID app), online banking, an e-ID card or Profil Zaufany (the free government e-ID);
• with a qualified electronic signature.

As the owner of a JDG you have full rights automatically; nothing to file. Your PESEL (national ID number) alone is never enough. If you are a foreigner still sorting out those logins, see which government login opens what.

Token or certificate? You need one only for software or for invoices issued offline.

Watch out: the KSeF regulation still says tokens work only until 31 December 2026. The Ministry’s KSeF FAQ says tokens will stay with no end date, but the regulation had not been amended by 24 September 2026. If your software logs in with a token, ask its provider before the year ends.

A company logs in with a qualified electronic seal carrying its NIP. Without one, it files ZAW-FA, a notice to the tax office naming one person (not necessarily a board member), who can then grant rights to others. You can file it on paper, through e-Urząd Skarbowy or through e-Doręczenia (official e-delivery). Since 1 January 2026, not through ePUAP (the older government portal).

Your accountant: log in, open permission management, choose the person or the accounting firm (by its NIP), and tick what they may do: issue invoices, view invoices, manage permissions. If you give the rights to the whole firm, it can pass them on to its staff.

What KSeF leaves out

Much of a freelancer’s paperwork never reaches KSeF:

• Foreign suppliers. Google, Meta, AWS, Adobe, GitHub or a foreign airline send PDFs by email or through a portal. See what KSeF won’t collect for you.
• Receipts. Until 31 December 2026, a till receipt with your NIP up to 450 PLN (or 100 EUR) gross counts as a simplified invoice and stays outside KSeF. From 1 January 2027 it is no longer an invoice: a business buyer who needs one gets it in KSeF. More in receipt or invoice.
• Most sales to consumers, which are voluntary in KSeF (above).
• Pro forma documents and orders, which are not invoices, and single-journey tickets that count as simplified invoices.

Your own invoices to foreign clients are the opposite case: they are issued in KSeF, and you send the client the PDF. See invoicing a client abroad.

So a month’s documents still come from two places. Komplet, our free Mac app, reads the PDFs, scans and photos that KSeF never sees and files each one into the right month under a readable name, ready for your accountant.

When do penalties start?

As the law stands on 24 September 2026:

They cover three mistakes: not issuing an invoice in KSeF when you had to, using the wrong format during a KSeF failure, and sending an invoice issued offline too late. They do not lead to a criminal tax case.

On 23 September 2026 a government draft (UD477) appeared that would move these penalties to 1 January 2028. The announced plan is for the tax office to remind taxpayers and check their settlements in 2027 instead of fining them. It is a draft, not law, and does not change the obligation to use KSeF from 1 January 2027.

Tip: if KSeF is down or you are offline, you can issue an invoice in offline24 mode and send it to KSeF by the next working day. Do not hand it to a Polish business buyer before it is in KSeF.

What to do next

1. Log in to the Aplikacja Podatnika KSeF and look at the invoices issued to your NIP.
2. Give your NIP to every Polish supplier, shops included, whenever you buy for the business.
3. Choose how you will issue invoices: the free app, e-mikrofirma, or invoicing software connected with a token.
4. If you still issue PDFs under the 10,000 PLN relief, move to KSeF before 1 January 2027. You can practise in the Ministry’s test and Demo environments.
5. Give your accountant permissions in KSeF, and agree who checks for new invoices, since KSeF will not tell you.
6. Keep collecting what KSeF leaves out: foreign invoices and receipts.