KSeF - What It Is and When It Becomes Mandatory

What is KSeF?

KSeF, the National e-Invoicing System (Krajowy System e-Faktur), is a nationwide IT system run by the tax administration. It is used to issue, transmit and store so-called structured invoices (faktura ustrukturyzowana) - that is, invoices in a uniform XML format. Instead of emailing a PDF to your counterparty, you issue the invoice in the system and it is automatically delivered to the recipient and to the tax authority.

A structured invoice has a predefined format and fields, which makes it readable both for a human and for accounting systems. As a rule, the moment it is issued and received is the moment a number is assigned in the system (the KSeF number).

When does KSeF become mandatory?

The obligation to use KSeF comes into force in stages:

• 1 February 2026 - large companies whose sales (including tax) exceeded PLN 200 million in 2024.
• 1 April 2026 - all remaining taxpayers, including those exempt from VAT, meaning most micro, small and medium-sized companies.
• 1 January 2027 - the smallest taxpayers, whose monthly sales value does not exceed PLN 10,000.

The obligation to receive invoices through KSeF applies to companies from the very first stage - even if you start issuing invoices later, you must be able to receive those that arrive in the system. KSeF could already be used voluntarily before that.

The dates on which the obligation takes effect have been postponed several times in the past, and some details (for example the deadlines for penalties) are still being clarified. For our clients we keep an eye on the schedule and inform them in advance of exactly when KSeF will apply to them.

How does issuing an invoice in KSeF work?

In practice the process looks as follows:

• You prepare the invoice in accounting software or a KSeF-compliant tool (in XML format).
• The invoice is sent to the KSeF system.
• The system assigns it a unique KSeF number and a date.
• The invoice is made available to the counterparty directly in the system.
• The document is archived in KSeF (as a rule for 10 years).

You no longer have to send invoices separately by email or worry about storing them - the system does that for you.

What does KSeF mean for small companies and sole proprietorships (JDG)?

Most sole proprietorships (JDG, jednoosobowa dzialalnosc gospodarcza) and smaller companies - including those exempt from VAT - were covered by the obligation from 1 April 2026, while the smallest taxpayers (sales up to PLN 10,000 gross per month) will be covered from 1 January 2027. In practice you need a tool for issuing invoices in the KSeF format - this can be accounting software, an application, or the free tools provided by the Ministry of Finance - and you need to be able to receive invoices from the system.

Benefits

• A shorter VAT (value-added tax) refund deadline - since 1 February 2026 the basic deadline is 40 days instead of 60.
• Fewer mistakes and no lost invoices.
• An end to paper and to manually forwarding documents.

Challenges

• A change to your existing invoicing process.
• The need to grant permissions (who issues and who receives invoices).
• No option to issue invoices “for the drawer” outside the system.

How to prepare your company for KSeF?

• Tidy up your counterparties' data, especially their tax identification numbers (NIP).
• Choose a KSeF-compliant tool for issuing e-invoices.
• Set permissions in the system - who in the company issues and who receives invoices.
• Train your team on the new process.
• Agree the flow of invoices and documents with your accounting office.

At Luno-Group you do not have to buy separate invoicing software - our client panel handles KSeF free of charge. You issue and receive invoices in one place, and we send them to the system and help set up the whole process so that the switch to the new rules is stress-free.

The most common mistakes when implementing KSeF

• Putting off preparations until the last minute.
• Not granting the accountant permissions in the system.
• Out-of-date counterparty data (incorrect NIP numbers).
• Treating a KSeF invoice like an ordinary PDF instead of a document with an official number.