The question of whether backdating an invoice is permissible recurs with every change in the method of documenting sales. With the introduction of the obligation for taxpayers to issue structured invoices in the National e-Invoice System (KSeF), this issue has taken on a new dimension. Some businesses assume that the KSeF technically prevents backdating. Others note that the system accepts an XML file with a date in the P_1 field earlier than the day it was submitted. Both assumptions are only partially accurate. In today's "Taxation to and from," we discuss how the law classifies such an invoice and the risks associated with issuing it.
General rule: two separate dates
The VAT Act distinguishes between the date of invoice issue and the date of delivery or service performance. Pursuant to Article 106e, paragraph 1, point 1 of the VAT Act, an invoice must include the date of issue, and pursuant to Article 106e, paragraph 1, point 6, the date of completion or completion of delivery, service performance, or receipt of payment, if such a date is specified and differs from the date of issue. The date of issue must reflect the date on which the document was actually created. Entering an earlier date here, typically coinciding with the date of sale, constitutes backdating and renders the invoice unreliable as to its date.
The time limits are set by Article 106i of the VAT Act. Generally, an invoice is issued no later than the 15th day of the month following the month of delivery or service provision, but no earlier than the 60th day before these events. Failure to meet the deadline does not affect the tax liability, which generally arises upon delivery or service provision. Therefore, a late invoice does not require a fictitious issuance date. However, it does require the tax to be reported during the tax liability period, if necessary through a JPK_V7 correction, along with payment of default interest.
Date of issue of the structured invoice
Pursuant to Article 106(1) of the VAT Act, a structured invoice is deemed issued on the date it is submitted to the KSeF. The buyer receives it on the date it is assigned an identification number in the system. Against this background, the thesis was formulated that the KSeF excludes backdating, as the date of issue is determined by the moment the file is accepted by the system.
This thesis requires significant clarification. Pursuant to Article 106nda, Section 16 of the VAT Act, a structured invoice is also considered an invoice issued offline24 if the date of its submission to the National Tax Information System (KSeF) is later than the date of issue indicated on the invoice. For such invoices, Article 106nda, Section 10, stipulates that the date of issue is the date indicated by the taxpayer. Therefore, the system will not reject a file with an earlier date in the P_1 field; only a future date is rejected. This position is confirmed by the Ministry of Finance in its responses to parliamentary questions and by the Director of the National Tax Information System.
Classifying an invoice as issued offline24 triggers the obligation to submit it to KSeF immediately, no later than the next business day after the date of issue. An invoice with the date in field P_1 preceding the submission date by more than one business day is therefore, by law, considered an offline24 invoice submitted after the deadline. KSeF does not verify the accuracy of the entered date, and responsibility for its accuracy rests with the issuer. Special circumstances (system failure, system unavailability) allow for late submission of an invoice, but do not justify entering a date when the invoice has not yet been issued.
Risks on the part of the issuer and the buyer
Article 106ni, paragraph 1, point 3 of the VAT Act provides for a fine for failing to submit an invoice to the National Tax Authority (KSeF) by the required deadline. The fine is based on the tax amount shown on the invoice, and for invoices without any tax shown, the upper limit is 18.7% of the total amount due.
This exclusion applies only to failure to meet the deadline, not to the accuracy of the invoice's content. An invoice that is incorrectly issued makes it unreliable within the meaning of Article 62 § 2 of the Fiscal Penal Code, which provides for a fine of up to 720 daily rates or imprisonment, or both.
On a material level, backdating does not change the seller's VAT settlement period, as defined by Article 19a, Section 1 of the VAT Act. However, it may affect the moment of revenue generation, which falls on the date of service provision, but no later than the date of invoice issuance or settlement. For the buyer, backdating does not accelerate the right to deduct, which arises no earlier than in the settlement for the period of invoice receipt, and receipt of the structured invoice occurs on the date the KSeF number is assigned. Therefore, postponing the submission to the next month postpones the deduction by the entire settlement period, which, given high tax amounts, burdens the contractor's liquidity. Discovering an understatement of liability resulting from untimely sales documentation during an audit may also result in the establishment of an additional tax liability under Article 112b of the VAT Act.
Practical conclusions
An invoice in the KSeF system may include a date in the P_1 field earlier than the date of transmission, but only if it corresponds to the date the document was actually prepared and the taxpayer submits it to the system in a timely manner. Therefore, the KSeF system does not constitute a technical blockade against backdating. However, it does permanently record both the date entered by the issuer and the date of transmission, and any discrepancy exceeding one business day is detectable from the system data itself.
If the deadline is missed, the invoice should be issued with the current date, indicating the actual day of delivery or completion, and the settlement should be corrected for the tax period. Invoicing processes should take into account the buyer's deduction shift at the turn of the month, and the use of offline24 mode should be covered by an internal procedure.
This article is for informational purposes only and does not constitute legal advice.
The law is current as of November 9, 2026.
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