KSeF mandatory. Find out who is affected by the National e-Invoice System and who needs to use KSeF 2.0

KSeF, or National e-Invoice System, changes one key thing: an invoice ceases to be just a file, and begins to act as a document in the system. In 2026, the use of KSeF will become mandatory in stages. From 1 February 2026, the obligation will cover entities whose sales in 2024 exceeded PLN 200 million including VAT. From April 1, 2026, the obligation will cover most of the others. The smallest can benefit from the simplification until 31 December 2026, if in a given month the total sales with VAT on invoices issued outside the KSeF does not exceed PLN 10,000. For this group, the full obligation will start from 1 January 2027.

In this article I explain what a KSeF is, who the mandatory KSeF applies to and how to find out from which date it applies to your case. No spilling water, no scaring. The very rules that affect whether you have to invoice in KSeF or if you can still issue invoices outside KSeF under simplification until the end of 2026.

Czyme is KSeF. National e-Invoice System at a glance

KSeF, or National e-Invoice System, is a state-owned platform for e-invoicing. Simply put, KSeF is a system in which an invoice is no longer just a PDF file sent by email. It becomes a document in the standard, which operates within the framework of the KSeF system and has an unambiguous identification.

In 2025, KSeF was still a solution that some companies used voluntarily. In the following stages, it will be necessary to use the KSeF when the obligation covers you. Then it becomes crucial that the document exists in the platform, and not just that it was generated in your program.

Structured invoice in KSeF. What does it mean for document circulation

In KSeF, the basis is a structured invoice, that is, a document saved in a data format, which the system can automatically verify. Such an invoice issued in the KSeF model functions as an e-invoice in KSeF, i.e. a document with a specific structure and processing path.

What this changes in the practice of document circulation:

— invoices in KSeF appear in the platform only after they have been correctly sent to KSeF
— the key moment is the acceptance of the document by the system, because then the KSeF gives it an identifier
— after acceptance, the document receives a KSeF number, i.e. a unique identifier, often described as the KSeF number of the invoice
— thanks to this, KSeF recognizes invoices unambiguously, and the document actually exists in KSeF and can be collected as an invoice from KSeF

Access to KSeF. How Authorization Works

The system distinguishes roles and allows you to assign rights to issue, receive and manage documents. In practice, this means that one person can issue documents and another can only view them or manage access.

For support, you can use tools provided by the platform, such as the KSeF Taxpayer App and mobile tools such as the KSeF mobile application. In any case, what matters is who has the permissions and how they are assigned to the organization and users.

KSeF system. What happens after the document is sent

Once the document is sent to the system, the issuance in the KSeF can be considered as a process with a clear final step: acceptance by the platform. After sending to the KSeF, the document is validated, and then it receives an identifier, that is, the KSeF number. Only then can it be said that the document is in the circulation of the platform.

On the technical side, many companies implement this through solutions integrated with KSeF. Such integration with KSeF is based on the KSeF API and operates within the infrastructure, including the KSeF production environment. Thanks to this, the document can be sent without manual login, as a document issued using KSeF in the accounting or invoicing system.

It is also worth remembering that the platform provides modes of operation in case of KSeF failure, because then the way of document circulation changes. From the user's perspective, the most important thing remains that the invoice is recognizable in the system by the KSeF number and can later be reproduced as an invoice from the KSeF.

KSeF — who it covers and to whom the obligation applies

If you ask “KSeF — who”, then the answer is simple: the obligation applies to taxpayers who, as part of their activity, issue invoices in accordance with VAT regulations. It is not about the invoicing program itself, but about the fact that the document is to go to the platform as an invoice structured in KSeF, that is, an e-invoice supported by the National e-Invoice System.

In practice, two elements are crucial: who is covered by the regulation and from when the obligation to use the KSeF begins to operate in a given case.

Who KSeF covers in the first place.

The mandatory KSeF enters in stages, so at the start it will cover the selected groups earlier and the others later. The most important dates are February 1, 2026 and April 1, 2026.

The simplest shot looks like this:

— February 1, 2026 is the moment from which the obligation covers taxpayers whose sales in 2024 exceeded PLN 200 million including VAT
— April 1, 2026 is an extension of the obligation to most other taxpayers
— until 31 December 2026, simplification is foreseen for the smallest. If in a given month the total sales with VAT on invoices issued outside the KSeF does not exceed PLN 10,000, they can benefit from this simplification until the end of 2026
— from 1 January 2027, the obligation will become fully operational for this group

The entrepreneur and the obligation to issue invoices. When you need to use KSeF

If you operate as an entrepreneur and you have situations where you need to document invoice sales, then the topic of KSeF concerns you directly. In KSeF, it is crucial that the document is to be accepted by the system as a structured invoice. Only then does the invoice receive an identifier, that is, the KSeF number, and the document itself becomes visible in the platform.

In practice, “you must use KSeF” means one thing: if you are obliged to issue an invoice, then within the framework of the new rules there is also an obligation to issue invoices in KSeF. That is, you not only issue a document, but you issue it in such a way that it goes to the system and is accepted. This is the essence of the new model.

It is worth remembering that the obligation also applies to taxable persons exempt from VAT. Exemption from VAT does not mean no invoicing. It means only a different way of accounting for tax. If invoices appear in your business, then at some point the rules of KSeF will also apply.

Whom it does not concern. When the use of KSeF is not

KSeF does not apply to those who do not have invoice obligations within the meaning of the VAT regulations. If there is no obligation to issue invoices in your business, then there is no obligation to use KSeF either.

There are also special situations in which the legislation provides for the possibility of invoicing outside the KSeF, for example in a transitional period for the smallest until the end of 2026, as well as in technical scenarios such as the failure of the KSeF. However, this does not abate the direction of change. It regulates only cases in which it is impossible to act in the standard mode or the legislator has provided a time for transition.

What does the date February 1, 2026 mean

The date of 1 February 2026 is the first moment when the mandatory KSeF begins to operate in stages. In short: from that date, some entities will no longer be able to consider e-invoicing as an option. KSeF from February 1, 2026 becomes standard for them, and sales documents will have to go through the National E-Invoice System.

February 1, 2026. For whom the obligation to use the KSeF starts

1 February 2026 concerns the first implementation group. This is the stage for the largest, indicated by the sales threshold for 2024. If your sales in 2024 exceeded PLN 200 million including VAT, then the obligation to use KSeF begins.

What is worth understanding practically:

This is not a “when is it worth” date. This is the date from when the KSeF will be mandatory for the first group
— if you are in this group, you must issue invoices in KSeF and send them to the system so that they are accepted and receive the KSeF number
The question is whether you meet the condition of the first stage. This can be checked in the sales data for 2024, because they are the ones who decide the start

If you do not catch yourself at the first stage, this does not mean peace for long. Another important date is April 1, 2026.

KSeF will be mandatory. What's changing for e-invoicing

When the KSeF obligation begins to work, one key thing changes: it does not matter to generate a document in the program itself. What matters is that the document has gone through the system. In practice, a structured invoice is considered to be issued only after it has been sent to the KSeF and accepted by the platform.

What does this mean in everyday operation:

— you must issue invoices as structured invoices, i.e. invoices structured in KSeF
— you can issue a document in KSeF or in an integrated system, but so that it is sent and accepted in KSeF
— after acceptance, the document receives an identifier, that is, the number of the KSeF. It is this number that confirms that the invoice is in the system
— in practice, the invoice “lives” in the platform. These are invoices in KSeF that you can download, not just a file from the mail

It is also worth distinguishing two things: the obligation to issue a document and the obligation to issue it in the appropriate channel. For many companies, the difference between “I put in the program” and “the system accepted and assigned the number” will be the biggest change.

Implementation of KSeF and KSeF service. Scope and requirements

The implementation of KSeF does not imply a single, rigid tool. You can work on solutions provided by the state or on commercial systems that are prepared for sending invoices to KSeF.

In practice, there are three areas that need to work:

Access and permissions. In order to issue documents, you need access to the KSeF for the right people and roles
— shipping channel. The document must go to the platform as an invoice to KSeF, that is, in a standard that allows acceptance in the system and assigning a number
— integration. If you are using an external system, it is important that it is integrated into the KSeF. Such integration with KSeF is often based on an API and works in a production environment

It is also important that the obligation applies to operation in the standard mode, but the legislation provides for exceptional scenarios, for example, in the event of a KSeF failure. Then the rules of circulation can change, but this does not remove the rule that the invoice should eventually go to the system.

April 1, 2026. KSeF from stage 1 to full scope

The date of 1 April 2026 is the moment when the e-invoicing obligation in KSeF is extended to a much wider group of entities. If earlier the question arose “who will KSeF cover”, then it is from this term that the answer becomes much more universal. In practice, KSeF has been moving from the “biggest first” model to the universal model from 1 April 2026, and for many companies this means a real start in the system.

In communication, the term KSeF 2.0 is often used, which is intended to emphasize a new stage in the functioning of the platform, the development of technical solutions and a wider scope of application. Regardless of the naming, the most important thing for the user is that from this date there is a growing group of entities that will have to use KSeF and for whom the use of KSeF will become a daily standard.

KSeF. What changes after the extension of the obligation

With the extension of the obligation, the change is simple but palpable: invoicing in more companies goes to a single channel, that is, to the platform. This means that sales documents will increasingly function as invoices in KSeF rather than as files transferred between parties.

In practice:

— the extent to which the obligation to use the KSeF applies to taxpayers issuing sales documents is increasing
— documents in circulation will more often be visible in the system as invoices in KSeF, and not only as attachments in emails
— more and more often you will encounter the situation that the contractor expects a document “from the system”, i.e. an invoice from KSeF, because this facilitates collection and archiving

At this stage, it is even clearer that KSeF is not just a new file format. It's a change in the way we act. The document does not exist “next to the system”. It is supposed to go to the platform, be processed and labeled with a number.

Scope of the second stage. What is included in the new implementation in practice

The second stage implies the extension of the duty to those who did not enter earlier in the first wave. For many companies, this will be the moment when the obligation to issue invoices in KSeF will cover their sales.

What does this mean from the side of duties:

— if you are required to document the sale with an invoice, then from this stage there is a requirement to issue it as a structured invoice in KSeF
— in practice, you will have to issue invoices in KSeF or use tools that allow sending invoices to KSeF
— the documents will have to go to the system in order to receive the ID and be considered to have been issued correctly
— if you issue sales documents, there is an obligation to issue invoices in KSeF, i.e. a model in which the document is to be structured and accepted by the platform

For many people, it will also be crucial to distinguish between standard circulation and exceptions. In certain situations, invoices may appear outside the KSeF. Such cases arise from a transitional period for the smallest until 31 December 2026 or from technical scenarios, for example, the failure of the KSeF, and not from the fact that the obligation disappears.

Differences between stages. What remains unchanged

Regardless of whether we are talking about the stage from February or from April, certain rules remain the same:

— the document must be accepted by the system. Exhibiting in your program alone will not be enough if the document is not sent to the KSeF and accepted
The key is the identifier. This KSeF number confirms that the document has been handled on the platform
— the invoice acts as a structured invoice, i.e. in a standard that allows automatic processing in the system
— in most cases, whether a document is “in order” is decided by whether it went to the platform and was accepted

From the naming side, you can meet the designations of the type KSeF 1.0 and KSeF 2.0, but for the user the main thing is that the principle of operation is the same. The system accepts the document, gives it a number and makes it available within the platform.

How to find out who is covered by the term in your case

If you are wondering who the obligation applies to and from when, it is crucial to separate two things: whether you are subject to the obligation to issue invoices at all, and whether in your case there is already an obligation to issue invoices in KSeF. It is this second part that answers the question “KSeF — who” and when.

To check this, it is worth relying on three pillars: the status of the taxpayer, the scale of sales for 2024 and whether you issue documents in circulation for which KSeF applies.

Most often it looks like this:

— if you are a taxpayer within the meaning of the regulations and as part of your activity you have to issue invoices, the topic of KSeF is relevant for you
— if in 2024 you exceeded the threshold of PLN 200 million including VAT, then KSeF from February 1, 2026 may apply to you from February 1, 2026.
— if the first stage does not cover you, and at the same time there is invoicing in your business, then the real date is KSeF from April 1, 2026, that is, the start of a wide range from April 1, 2026.
— if you are entering a transitional period for the smallest, then simplifications may apply until the end of 2026. In such a variant, it is possible to issue invoices outside the KSeF provided that in a given month the total sales including VAT on these invoices does not exceed PLN 10,000. The transition period runs until December 31, 2026.
— after the end of the transitional period, i.e. from 1 January 2027, the obligation will become fully operational also for this group

In practice, the verification comes down to whether you enter the group covered by the stage from February or from April, and if in your case the simplification works until the end of 2026.

It is also worth remembering that the very fact of issuing a document is not everything. In the KSeF model, what matters is whether the document has been accepted by the system. For many companies, the biggest change will be that the invoice is supposed to be in the system, not next to it:

— if you have an obligation, then you need to issue invoices in KSeF, and not just create a document in your program
— the invoice is recognized in the system if it has been correctly sent to KSeF and accepted by the platform
— in practice, the confirmation is the number. If the invoice has a KSeF number, it means that the document has been accepted and can be considered as issued in the system

Altera.app. If the KSeF is to be mandatory, it is good to have order in the invoices

If you know that KSeF will become mandatory steps, it is worth having a tool that organizes invoices and documents faster than manually rewriting and searching for attachments in emails. Altera.app is an application that combines sales invoicing, electronic invoice circulation, communication around documents and payment preparation in one place.

What you can have on hand in Altera.app:

— 🚀 Instantly issue and send sales invoices
— 🤖 intelligent AI-based OCR to read data and items from cost invoices and organize documents
— 🧩 electronic invoice flow with acceptance paths, full visibility of statuses and matching of user accesses
— 💬 messages and comments on invoices and a secure archive of communication history
— 💸 packages of transfers for import to the bank and monitoring of receivables, liabilities and payment deadlines
— 📊 Finance Preview, which facilitates quick insight into income and expenses

If you want to see how it works in practice, test Altera.app and see if this way of working fits your billing process.

summary

KSeF will be mandatory, but not for everyone at the same time. The most important thing is to determine whether you enter the stage from February 1, 2026 or only from April 1, 2026, and whether you are subject to an exception with the limit of invoices outside the KSeF until December 31, 2026. In KSeF, it is not only the issuance of the document that counts, but also that the invoice actually exists in the KSeF and has a KSeF number.

The main thing to remember:

— 📅 On February 1, 2026, the obligation for entities with high sales for 2024 starts
— 📅 On 1 April 2026, the obligation covers a wide market, with the exception of the smallest in the transitional period
— 🧾 invoices in the KSeF are recognized only after sending to the KSeF and assigning the KSeF number
— ⏳ until 31 December 2026, a transitional solution for the smallest is in operation, and full obligation for them will enter from 1 January 2027.

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