Starting April 1, 2026, the vast majority of Polish entrepreneurs are required to issue structured invoices under the National e-Invoice System (KSeF). Although this system was intended in theory to provide a painless solution to the tax system, in practice it has become a source of many uncertainties. In this article, we will attempt to explain how KSeF works for sole proprietors and answer all commonly asked questions.
What regulations introduce and regulate KSeF?
The legal foundation for the National e-Invoice System is the VAT Act, specifically Articles 106ga to 106ni. It is the Value Added Tax Act that defines the system itself and introduces a number of very detailed requirements regarding the use of the National e-Invoice System.
The KSeF is also mentioned in the provisions of other acts, such as the Tax Ordinance Act or the KAS Act, but these are technical regulations that do not carry any real implications in economic practice.
When do you need to use KSeF?
The process of implementing the National e-Invoice System took several years – its implementation was phased.
Starting in 2022, the use of the KSeF was optional. Initially, however, only a small group of entrepreneurs used the system. In our opinion, this was due to the relatively high level of uncertainty observed in the Polish business environment. Due to the significant delay in implementing the entire program, which was originally scheduled to take effect in 2024, a significant number of Polish entrepreneurs probably hoped that the government would abandon these changes.
Mass, voluntary implementation of this solution became visible only at the turn of 2025 and 2026, when it was already known that the KSeF would definitely come into force. taxpayers with a turnover exceeding PLN 200 million per year had time to switch to issuing structured invoices until February 1, 2026, many of them did so 2-3 months earlier. Smaller entrepreneurs had 2 months more, although there were also those among them who implemented the changes well ahead of schedule.
The smallest taxpayers, whose monthly B2B sales (including VAT) do not exceed PLN 10, may issue paper invoices until the end of 2026.
Penalties for failure to comply with the obligation to use KSeF
Given the doubts and difficulties raised by the National e-Invoice System, it was decided to postpone the application of penalties. Sanctions for failure to issue invoices in the system will only apply from 1 January 2027.
After the transition period, A taxpayer who, despite the obligation, issues an invoice outside the KSeF may be fined up to 100% of the VAT amount shown on the invoice. In case of exempt taxpayers, This limit is 18.7% of the total amount due. Importantly, however, the penalty under Article 106 does not apply to situations in which issuing an invoice was possible. Issuing a paper document in the event of a System failure is, of course, permissible, although it must be entered into the KSeF after the system returns to normal operation.
It's worth noting that the taxpayer's situation will depend on whether they fail to issue a structured invoice or fail to do so at all. If the sale is not documented either in the National Tax and Financial Register (KSeF) or with a paper invoice, the taxpayer is also exposed to sanctions under the Fiscal Penal Code. According to Article 62 of the Fiscal Penal Code, the fine for failing to issue an invoice or issuing a defective document is up to 180 daily rates. For unreliable invoices, the penalty increases to 720 daily rates. Daily rates are calculated based on the perpetrator's financial situation, but by failing to issue invoices, a high-income individual must consider the threat of a fine exceeding 100 PLN. The fine does not exempt the perpetrator from the obligation to repay any taxes due if the offense is proven.
The absence of sanctions is not consent
While searching for information about the KSeF system online, we came across an exceptionally dangerous phenomenon. Some entrepreneurs, aware that there will be no penalties for failing to issue structured invoices in 2026, are deliberately not issuing documents in the system. Contrary to appearances, such behavior poses significant risk to taxpayers.
During verification or audits, the authority will almost certainly raise doubts about invoices that were issued in paper or electronic form, contrary to the requirements. In our opinion, there is a very high risk of allegations being raised against the taxpayer that they maintained their records in an unreliable manner or attempted to obtain an unauthorized tax advantage.
Even if the taxpayer ultimately proves their case in the administrative court, failing to use the KSeF, despite its mandatory nature, will result in high costs and a stressful dispute with the tax authority. As a result, the absence of penalties for not using the KSeF can never be considered as permission to fail to comply with the obligation.
Is every gainful activity subject to KSeF?
This issue also requires clarification and clarification. First of all, it is worth pointing out that the obligation to issue structured invoices in KSeF is not affected by the status of the VAT payer. The Goods and Services Tax Act does not link VAT registration with structured invoices in any provision.
The obligation to register with the National Tax Administration (KSeF) is not affected by the chosen form of taxation. Therefore, invoices in the System must be issued by taxpayers who are subject to taxation. scale, rulerAnd lump sumIt's also worth noting that taxpayers conducting unregistered business can, and sometimes must, use the KSeF. To do so, they must first obtain a Tax Identification Number (NIP).
The matter becomes somewhat more complicated when a taxpayer derives income from private rentals (e.g., real estate or machinery to their company). Generally, it is assumed that if the taxpayer's business involves providing property to private individuals for a fee, the obligation to issue invoices in the National Tax Information System (KSeF) does not arise. However, in an interpretation issued on February 4, 2026, the Director of the National Tax Information System (KIS) indicated that individuals renting premises to businesses are already obligated to use the System. It is irrelevant that this is still a private rental, which does not meet the definition of a business activity under business law.
Issuing an invoice by KSeF
The implementation of the National e-Invoice System brings significant changes to the way documents are issued. Besides the obvious difference of completely digitizing this process, there's also the issue of submitting invoices to the National e-Invoice System. Let us note that under the provisions of the VAT Act, an invoice becomes a valid, existing document only when it is validated and assigned a KSeF number.
The entry into force of the National System for VAT does not fundamentally change the general deadline for issuing an invoice, which is the 15th day of the month following the month of delivery or service provision. However, the National System introduces several additional rules.
In the case of the so-called online mode (normal functioning of KSeF) what counts is date of dispatch, as per Article 106(1) of the VAT Act. Therefore, it is irrelevant when the system assigns the document number. Although this usually happens within a few minutes, it is relevant if the taxpayer issues an XML invoice, for example, on January 31st at 23:58 PM. Assigning a number in February, 10 minutes after midnight, will in practice be irrelevant, and the tax consequences for the issuer will be attributed to January, not February.
On the other hand, the date of acceptance will be the moment when KSeF positively verifies the file and assigns it a system number. This moment, in turn, is the date the domestic buyer receives the invoice. The moment the taxpayer logged into the system or the day they downloaded or entered it into their accounting records is irrelevant.
Importantly, if a seller issues an invoice incorrectly and the system rejects it, it is assumed that the invoice was not issued. Consequently, the issuance date will be the date the document is resubmitted to the KSeF.
KSeF and invoices issued after the deadline
In the past, issuing invoices late was a very common practice. Typically, it followed the following pattern:
- The entrepreneur provided his services during a good period, for example from August 1 to 31,
- On August 31, he informed the contractor about the scope of work performed and the agreed amount,
- The settlement was accepted or rejected, which often took several or a dozen days,
- The document was issued, for example, on September 17, so it could be included in the August settlement of income tax advances and VAT settlement.
The motivation behind not declaring the actual date of issuance was tax considerations. This could have resulted in the total taxes due in September being disproportionately small compared to the amount payable in October. Seeking to minimize these fluctuations, which clearly had a negative impact on financial liquidity, entrepreneurs often issued invoices on a later date than the declared date.
The introduction of the KSeF has made it virtually impossible to use this mechanism. The invoice must be sent immediately, no later than the next business day after its issuance.
KSeF and invoices issued in PDF format
It should be noted that the implementation of the National e-Invoice System did not result in the complete withdrawal of PDF invoices – entrepreneurs still send documents in this form, if only because emails remain the main tool for business communication. However, it should be clearly stated that PDF may only be a visualization of an invoice, but under the provisions of the VAT Act it will never replace a structured XML document.
The Director of the National Tax Information has already commented on the issues related to the introduction of invoice visualizations into circulation. As it results from the interpretation of May 5, 2026, any deviations in the visualization's content from the original structured invoice may result in the visualization being considered a second document, which will result in double taxation. The taxpayer's question concerned seemingly trivial details, such as replacing "item description" with "product name." Although, in our opinion, at the stage of the dispute in court, the taxpayer would be able to effectively demonstrate that the second invoice was not introduced into circulation, we would like to point out that Issuing invoice visualizations in PDF format is only possible if their content is identical to the XML file. Any deviations from this rule create additional, unnecessary tax risks.
Issuing invoices in KSeF for foreign contractors
Invoicing foreign contractors through KSeF is one of the most problematic issues and also requires clarification. KSeF is a binding system for Polish invoice issuers, and the buyer's access to the System is irrelevant in this case. When issuing an invoice to a German, Dutch or American contractor, you must use a KSEF.
However, there are no obstacles to recording and recognizing the cost of purchasing a service or goods from a foreign contractor who, for obvious reasons, will not document this transaction with an invoice.
An exception to this rule is a situation in which a foreign taxpayer has a Polish Tax Identification Number (NIP) and is registered for Polish VAT. In such a case, due to the lack of a registered office or permanent place of business in Poland, such an entity is not obligated to use the National e-Invoice System, although it may voluntarily join it.
Invoice received outside KSeF and the right to deduct
The Ministry of Finance explicitly states that the consequences of failing to comply with the obligation to use the KSeF system generally fall on the invoice issuer, not the purchaser. This, in turn, means that when receiving a paper invoice, the taxpayer still retains the right to deduct input VAT – provided, of course, all other conditions are met. However, as a general rule, it should be assumed that, for the purposes of the right to deduct, it is irrelevant whether the seller issued a structured invoice or not.
Is KSeF changing the rules for issuing advance invoices?
The introduction of the National e-Invoice System did not fundamentally change the rules for issuing advance invoices, although a few nuances worth noting emerged. Above all, it's worth remembering that, as a rule, VAT is payable upon receipt of payment. In such a situation, the invoice issuance date is secondary, and the statutory deadline of 15 days from the end of the month applies.
Invoice corrections and KSeF
One of the consequences of introducing the National e-Invoice System is a change in the method of correcting documents.
While the material basis for plus and minus corrections has not changed, corrective documents must also be issued in the KSeF system. The introduction of the System means that once an invoice has been issued, it is no longer possible to edit it without issuing a correction, even if the changes are merely cosmetic. This is important because, in practice, Corrective notes were completely withdrawn from circulation. Even if you make a mistake when entering the contractor's name, a correction is sent to the system.
Procedure in the event of a KSeF failure
During the implementation of the National e-Invoice System, many concerns arose about situations in which the system operated by the Ministry of Finance would fail, or if problems were localized and occurred on the invoice issuer's side. Surprisingly, legislators anticipated these events – several pre-determined procedures exist.
Local failure on the entrepreneur's side - offline24
In situations where the outage is local in nature (e.g., internet outage in the office, computer failure, accounting software malfunction), the so-called offline24 mode under Article 106nda of the VAT Act applies. In such a situation, the taxpayer is obligated to prepare an invoice consistent with the FA (standardized) logical structure, provide all necessary data, and forward the document to the buyer outside of the KSeF (KSeF), if necessary. The invoice itself must be entered into the KSeF immediately, no later than the next business day after its issuance.
In the case of invoices issued in offline24 mode, the date of issue of the document is the date of creation of the invoice, not the date of sending it to KSeF
Planned maintenance work at KSeF
Despite its short period of existence, KSeF has already undergone several maintenance works, mainly in January and February 2026. In a situation where previously planned updating, maintenance or repair works result in the unavailability of the System, entrepreneurs are obliged to issue structured invoices and, similarly to a local failure, send the invoice to KSeF no later than the next business day after the end of the System unavailability.
Official KSeF failures
During the official outage, taxpayers will be required to use the emergency mode, regulated by Article 106 of the VAT Act. Under this mode, invoices are issued outside of the active connection to KSEF and, similarly to offline24, must comply with the mandatory document template. After the outage ends, taxpayers have seven business days to upload their documents to the Ministry of Finance servers.
Official failure messages will appear in the Ministry of Finance's public information bulletin and in the KSeF application.
Permissions to use KSeF
Typically, sole proprietors use the KSeF system independently, but regulations allow for the granting of authorizations and delegation of authority to other persons. Typically, these will be delegated employees or accounting offices.
Taxpayers can grant KSeF authorization on behalf of their businesses using the ZAW-FA form at the e-tax office. The entire process takes just a few minutes, and the person receiving the authorization typically gains access to their KSeF profile within a day or two. However, this doesn't happen automatically.
Invoicing programs within KSeF
During the debate on the National Labor Inspectorate (PIP) reform, many noted the ease with which authorities will be able to identify businesses that regularly issue only one invoice per month, especially always to the same contractor. The National Labor Inspectorate (KSeF) will indeed facilitate the analysis of such cases, as the tax administration will have real-time access to structured data on the frequency of invoicing, remuneration values, service descriptions, and entities involved in transactions. This will allow for much faster identification of individuals who are, in practice, full-time employees.
This doesn't mean, however, that issuing a single invoice per month will automatically lead to an inspection or questioning of the B2B contract. This is one factor that may attract the attention of authorities, but it doesn't in itself determine the existence of a hidden employment relationship. Many entrepreneurs actually perform services exclusively for a single large client, for example, by implementing a long-term project, or by collectively billing all activities performed in a given month. This model of cooperation can be fully justified economically, especially if the contractor organizes their work independently, is responsible for its results, can use a substitute, has their own tools, and bears the risks associated with their business, thus simply meeting the requirements of the so-called entrepreneur test.
For those working on B2B contracts, a ministry-issued invoicing application will usually be a completely sufficient solution. Therefore, using paid programs may be unnecessary unless the entrepreneur requires additional features such as automatic payment settlement, integration with accounting, tax limit control, or report preparation. In practice, however, a free solution will often prove to be the most convenient.
