The introduction of KSeF (National e-Invoicing System) has given businesses new options, but it has also raised a number of practical questions. One of the most frequent is how the invoice issue date changes when the invoice is sent to KSeF. The issue becomes particularly important when an invoice is generated in the accounting system on one day and sent to KSeF the following day.
Understanding the rules on the issue date of e-invoices is essential for settling VAT correctly and keeping accounting records. Since 1 February 2026 the answer follows directly from the VAT Act, which, after KSeF became mandatory, treats an invoice sent to the system later than the day shown on it as the issue date differently.
Basic information about the National e-Invoicing System
The National e-Invoicing System was launched on 1 January 2022 as an optional solution for businesses. Since 1 February 2026 it has been mandatory for taxpayers whose sales including tax exceeded PLN 200,000,000 in 2024, and since 1 April 2026 for all other taxpayers (Article 145l of the VAT Act). The system is a modern IT tool for issuing, receiving and storing invoices in structured form. The whole system is administered by the Head of KAS (National Revenue Administration).
Until 31 January 2026 KSeF was optional. From 2026 it is mandatory, and until 31 December 2026 invoices outside KSeF may still be issued by taxpayers whose sales including tax documented by invoices in a given month do not exceed PLN 10,000 (Article 145m of the VAT Act). Invoices issued through KSeF receive a unique identification number assigned automatically by the system. As a result, every e-invoice has its own unique identifier in the system
The system does more than issue invoices. KSeF is used above all for end-to-end handling of electronic invoicing, covering the issuing, receiving and long-term storage of documents. It also allows the Head of KAS to analyse and check the accuracy of data contained in structured invoices.
When using KSeF, the issuer of an e-invoice receives detailed information about the invoicing process. This includes the date and time the structured invoice was issued, together with the identification number assigned by the system and the exact date and time it was assigned. If there are problems, the system also reports the date and time an invoice was rejected because it does not match the applicable schema, and the inability to issue an invoice when KSeF is unavailable.
KSeF can be used by taxpayers, entities they designate, enforcement entities and natural persons designated by those entities. The system also serves natural persons named in a notification granting permissions to use KSeF. All of them must be authenticated in the manner set out in the implementing regulations
Legal rules on the invoice issue date
The basic rules on deadlines for issuing invoices are set out in Article 106i section 1 of the VAT Act. Under this provision an invoice must be issued no later than the 15th day of the month following the month in which the goods were supplied or the service was performed. This is the general rule, and the law provides exceptions to it (Article 106i sections 2–8 of the VAT Act).
The mandatory elements of an invoice listed in Article 106e section 1 point 1 of the VAT Act include its issue date. This element is fundamental for settling VAT correctly and for keeping accounting records.
A specific rule is set out in Article 106na of the VAT Act, which applies directly to structured invoices, i.e. e-invoices issued through KSeF. It provides that a structured invoice is deemed issued on the day it is sent to KSeF. Since 1 February 2026 this rule has an exception: if the date of sending to KSeF is later than the issue date shown on the invoice (field P_1), the invoice is treated as an invoice issued in offline mode (Article 106nda section 16 of the VAT Act), and its issue date is the date in field P_1 (Article 106nda section 10).
A structured invoice is deemed received through KSeF on the day the system assigns it an identification number. This means that the moment the buyer receives the invoice is clearly determined by KSeF. The process is fully automated and requires no additional action from the parties to the transaction
Structured invoices are issued and received using special interface software, which is governed by Article 106gb sections 1 and 2 of the VAT Act. This software is the bridge between businesses' internal accounting systems and the central KSeF system. Where an accounting office handles the invoices, it needs the appropriate KSeF permissions for accounting offices.
The problem of changing the invoice issue date in KSeF
The most common problem with changing the invoice issue date arises when a business generates an invoice in its internal accounting system on one day but sends it to KSeF only the next day. For example, an invoice may be generated on 31 January but sent to KSeF on 1 February.
This raises serious questions about which date should be treated as the issue date for VAT purposes. The problem matters most when issuing the invoice and sending it to KSeF fall in different settlement periods, for example in different months or quarters.
Until 31 January 2026 the issue date of an e-invoice was determined solely by Article 106na section 1 of the VAT Act – it was the day of sending to KSeF, even if an earlier date had been entered in field P_1. Since 1 February 2026 the Act resolves this situation differently (Article 106nda sections 10 and 16)
Entering in field P_1 a date earlier than the date the invoice is sent to KSeF is not a reason for the system to reject it. Since 1 February 2026 such an invoice is treated as an invoice issued in offline mode (Article 106nda section 16 of the VAT Act): the issue date is the date in field P_1, and the taxpayer must send the invoice to KSeF without delay, no later than the next working day after the day it was issued (Article 106nda section 2).
Position of the Ministry of Finance
On the ksef.podatki.gov.pl portal the Ministry of Finance explains that for an invoice issued in offline24 mode (Article 106nda of the VAT Act) the issue date is the date shown in field P_1, and the invoice must be sent to KSeF no later than the next working day. A structured invoice sent to KSeF later than the day shown in field P_1 is also treated as such an invoice.
These rules should be reflected in accounting systems, especially where the invoice issue date affects the date on which a transaction is recorded in the accounts. Businesses should adapt their internal procedures and IT systems to these provisions
As a result, since 1 February 2026 the issue date of an e-invoice is the day it is sent to KSeF, and where an invoice with an earlier date in field P_1 reaches KSeF later – the date in field P_1, provided the invoice is sent within the deadline in Article 106nda section 2. Sending it after that deadline breaches this provision, and from 1 January 2027 the head of the tax office (urząd skarbowy) may impose a financial penalty of up to 100% of the tax shown on the invoice (Article 106ni section 1 point 3 of the VAT Act).
The problem is less significant when issuing the invoice and sending it to KSeF take place in the same settlement period, for example in the same month or quarter. Greater complications arise when the two events fall in different settlement periods.
Consequences for bookkeeping
The rules for determining the issue date of an e-invoice (the day of sending to KSeF or, if sent later, the date in field P_1) have significant consequences for bookkeeping. Above all, businesses need to adapt their internal accounting systems to these provisions.
Remember that an invoice sent to KSeF cannot be edited or deleted – errors, including in the date, can be corrected only with a corrective invoice. This is why the date in field P_1 and the moment of sending to KSeF must be settled before the document is sent.
Adapting internal accounting software to KSeF requirements should include synchronising invoice issue dates with the moment invoices are sent to the system. This helps avoid discrepancies between the data in the internal system and the official issue date of the invoice in KSeF
For VAT purposes it is crucial to assign the invoice to the correct settlement period. If an invoice dated the last day of the month in field P_1 is sent to KSeF on the next working day, which already falls in the new month, its issue date remains the last day of the previous month. The buyer, however, receives it only on the day the KSeF number is assigned, i.e. in the new month (Article 106nda sections 10 and 11 of the VAT Act).
Practical aspects of issuing e-invoices
Issuing invoices in KSeF requires businesses to understand how the process works. The first step is to enable the KSeF integration in the accounting software you use. This usually requires the relevant permissions and authentication in the system.
Once the integration is enabled, you can start issuing e-invoices. The process involves the following steps:
- Preparing the invoice data in the accounting system
- Checking that all required elements are correct
- Generating the invoice in structured format
- Sending the invoice to KSeF
- Waiting for confirmation of acceptance and assignment of the identification number
In many accounting systems integrated with KSeF you do not have to enter the issue date manually – the software fills in field P_1 with the date the invoice is sent to KSeF. If the invoice is sent on the same day, the issue date on the printout, in field P_1 and in KSeF is identical
After the invoice has been successfully sent to KSeF, i.e. processed by the system, it is deemed issued and receives a system identification number. The document also becomes available in KSeF on the buyer's side, and the buyer can download it and import it into their own accounting system.
Impact on VAT settlements
The rules on the issue date of e-invoices in KSeF have a direct impact on VAT settlements. Assigning the invoice to the correct settlement period is crucial for calculating tax liabilities correctly.
For the seller, the tax point arises as a rule when the goods are supplied or the service is performed (Article 19a section 1 of the VAT Act), not when the invoice is issued – a delay in sending to KSeF alone usually does not shift output VAT. The invoice issue date determines the tax point, among other things, for supplies of energy and gas, telecommunications services, rental, lease, leasing and ongoing legal and office services (Article 19a section 5 point 4). For the buyer, the right to deduct arises no earlier than in the period in which the invoice was received (Article 86 section 10b point 1), i.e. on the day the KSeF number is assigned – so a later sending may move the deduction to the next month, which matters for cash flow.
| Scenario | Date in field P_1 | Date sent to KSeF | Issue date | Consequences |
|---|---|---|---|---|
| Scenario 1 | 31 January | 31 January | 31 January | No problems |
| Scenario 2 | 31 January | 1 February | 31 January (offline mode) | The buyer receives the invoice in February |
| Scenario 3 | 30 September | 1 October | 30 September (offline mode) | The buyer receives the invoice in Q4 |
| Scenario 4 | 31 December | 2 January | 31 December (offline mode) | The buyer receives the invoice in January of the following year |
Be particularly careful when an invoice is dated the last day of a settlement period but is sent to KSeF in the following period. Such an invoice must reach KSeF no later than the next working day (Article 106nda section 2), and the buyer can deduct VAT from it no earlier than in the period in which it was received
For businesses that settle VAT quarterly, the issue may be even more important, especially for invoices issued at the turn of a quarter. Receiving the invoice in the next quarter shifts the buyer's deduction, and for services where the tax point arises when the invoice is issued, the seller's settlement period is determined by the issue date.
Recommendations for businesses
To avoid problems with changing the invoice issue date in KSeF, businesses should put appropriate procedures in place and adapt their accounting systems. The key point is that the issue date is the day the invoice is sent to KSeF or – if it is sent later – the date in field P_1, provided the invoice is sent within the deadline.
The basic recommendations include:
- Synchronising the generation and sending of invoices to KSeF
- Adapting internal accounting systems to KSeF requirements
- Regularly monitoring the status of invoices sent
- Introducing control procedures to prevent delays in sending
- Training the staff who handle invoicing
Pay particular attention to invoices issued in the last days of settlement periods. In such cases consider sending the invoice to KSeF on the same day it was generated in the internal system. This helps avoid shifting the buyer's VAT deduction and the risk of missing the sending deadline
Businesses should also update their accounting systems regularly to ensure full compatibility with KSeF. Accounting software providers keep introducing improvements to streamline the e-invoicing process.
Monitoring and process control
Using KSeF effectively requires appropriate monitoring and control mechanisms. Businesses should regularly check the status of invoices sent and respond to any problems.
KSeF gives businesses access to detailed information on the status of each invoice sent. This includes confirmations of acceptance, notices of rejection and details of the identification numbers assigned.
Practical example: A trading company issued an invoice dated 31 March (field P_1) for goods delivered in March, but because of technical problems sent it to KSeF only on 1 April, the next working day. The issue date remains 31 March, and the seller's tax point arose on delivery in March. The buyer received the invoice on 1 April (assignment of the KSeF number), so it can deduct input VAT no earlier than in its return for April, or – if it settles quarterly – for the second quarter.
Setting up alerts and notifications can help identify cases where invoices have not been sent to KSeF on schedule. This allows a quick response and minimises the impact on tax settlements
Regular reviews of invoicing processes help identify areas for improvement and streamline the whole system. Pay particular attention to invoices issued during busy periods, such as the end of a month or quarter.
