Mandatory KSeF: How to prepare your business in 2026

The obligation to issue invoices in KSeF is being implemented in stages, while the obligation to receive them in the system began on February 1, 2026. Switching to KSeF changes not only the document format, but also permissions, invoice circulation, error handling and actions in the event of lack of access to the system.

The information below is general in nature. The scope of the obligation for a specific transaction should be confirmed with an accountant or tax advisor.

What is KSeF

The National e-Invoice System is an IT system of the tax administration used to issue, receive and store structured invoices. A structured invoice is in the form of data consistent with a logical structure, not an ordinary PDF file.

KSeF 2.0 uses the FA(3) structure. After sending the correct document, the system assigns it the number KSeF. PDF may be a clear visualization of an invoice, but in the case covered by the obligation it does not replace a structured document.

Deadlines for mandatory invoicing

The implementation is carried out in stages:

• from February 1, 2026 - for taxpayers whose sales value, including tax, exceeded PLN 200 million in 2024;
• from April 1, 2026 - for other taxpayers, taking into account statutory exceptions and transitional solutions;
• from January 1, 2027 - also for taxpayers benefiting from a transitional facilitation for sales documented with invoices issued outside KSeF until the end of 2026, up to PLN 10,000 gross per month.

The obligation to receive invoices via KSeF began on February 1, 2026. Financial penalties related to incorrect issuance of invoices in KSeF are planned from January 1, 2027; Postponing penalties does not extend the deadline for the obligation itself.

Current stages and conditions are published by the Ministry of Finance on the website Implementation stages KSeF.

Important transitions and exceptions

Until the end of 2026, among other things, facilities are provided for taxpayers whose total monthly sales value, including tax, documented with invoices issued outside KSeF, does not exceed PLN 10,000. After exceeding the limit, the obligation arises from the invoice with which the limit was exceeded.

Until the end of 2026, the possibility of issuing invoices using cash registers and accepting fiscal receipts with NIP up to PLN 450 for simplified invoices has been maintained. Invoices issued to consumers are not covered by the mandatory KSeF, although they can be issued voluntarily in the system.

This is not a complete catalogue. The scope of the mandatory KSeF depends on, among other things, the status of the parties and the type of transaction. For official explanations, see section Scope of mandatory KSeF.

Offline24 mode, unavailability and failure

The regulations distinguish several situations that are commonly called "KSeF failure". Offline24 mode, announced system unavailability, failure and total failure have different rules for document marking and deadlines for its submission.

The company procedure should specify:

• who decides which mode to use;
• how to issue a document compliant with FA(3);
• how to generate the required QR code;
• how and when to deliver the document to the buyer;
• who is responsible for the subsequent sending of the invoice to KSeF;
• how to detect a document that has not been accepted.

Details of the mode are described on the official website Offline mode24.

Permissions and authentication

Before going into production, you need to determine who can issue, receive and view invoices and who grants further permissions. You should not use a joint account for several employees.

Depending on the legal form and method of representation, first rights may require a different procedure. Access can be performed using the methods provided by KSeF, and integrated systems can use appropriately secured authentication mechanisms. Current methods must be confirmed in the documentation of the Ministry of Finance.

The company should keep a register of granted authorizations and have a procedure for immediately withdrawing them after a change of position or termination of cooperation.

Three ways to work with KSeF

Free tools of the Ministry of Finance

They may suffice for a simple process and few documents. Their usefulness should be assessed in practice, taking into account the time required for manual data entry, handling corrections, receiving purchase invoices and replacing an employee.

There is no universal number of invoices at which this solution ceases to make sense. The limit depends on the complexity of the company's documents and process.

Invoicing program with KSeF support

May be suitable for a company that needs to more efficiently issue and receive invoices, but does not require integrated warehouse, production or advanced accounting. Before choosing, you need to check the scope of supported documents, emergency modes, permissions management, data export and manufacturer support.

ERP system with KSeF integration

ERP can link an invoice to an order, warehouse release, billing and accounting. Such an implementation is justified when the company needs a broader organisation of processes, and not just sending a file to KSeF.

KSeF alone is not a sufficient reason to purchase a powerful ERP. The decision should be preceded by an analysis of requirements, costs, data migration and maintenance. We describe the signals justifying such a project in the article about when to implement ERP.

What to verify in current firmware

The commercial information "we support KSeF" is not enough. It's worth asking your supplier specific questions:

• Does the software support FA(3) and all document types used by the company?
• How does document rejection present itself and who receives the alert?
• How does it handle corrections, attachments and special modes?
• Does it collect purchase invoices and prevent double posting? How does
• store credentials, KSeF, and communication history?
• How does it distribute user permissions?
• What does data export and the supplier change procedure look like?
• Who is responsible for updates after a schema or API change?

The scope and conditions of the enova365 licence and any other product should be confirmed in the manufacturer's current offer. You should not assume that all KSeF features are available in every configuration or without additional work.

Company preparation plan

1. Set the scope of the transaction. Divide documents by seller status, buyer status and sale type.
2. Describe the current circulation. Specify who creates, approves, sends, receives and posts invoices.
3. Select tool. Compare features, integrations, cost, support and exportability.
4. Grant minimum permissions. Separate administration from daily document handling.
5. Prepare unique scenarios. Include invoice rejection, internet outage, KSeF unavailability and employee absence.
6. Test integration. Check not only for correct document, but also for incorrect data, correction and re-operation.
7. Agree the process with accounting. Especially receipt of documents, assignment, corrections and period closing.
8. Train users. The manual should show normal operation and error handling.
9. Monitor your first periods. Check whether all documents have achieved the expected status.

Frequently asked questions

Does KSeF apply to sole proprietorship?

The sole proprietorship form in itself does not exclude you from KSeF. Taxpayer status, type of transaction and applicable exceptions matter. The specific case should be assessed in accordance with current regulations.

Is it still possible to send a PDF to the client?

PDF can be an additional visualization, but it does not replace the structured invoice in a transaction covered by the mandatory KSeF. The method of transferring the document also depends on the status of the buyer and the type of transaction.

Does KSeF replace archives and copies of accounting data?

KSeF stores structured invoices for the period specified in the regulations, but the company still needs continuity of its own processes, related data, configurations and documents that do not go to KSeF. The scope of the copies should be agreed with accounting and the system administrator.

Summary

Preparation for KSeF includes transaction analysis, tool selection, granting permissions, tests and procedures in the event of errors and unavailability. The most important thing is the correct operation of the entire workflow, not just sending a sample invoice.

NexaIT implements enova365 and KSeF integrations after analysing the customer's process. Contact usif you need an assessment of your current solution or implementation plan.