With the introduction of the mandatory KSeF, the area of corrective invoices takes on an entirely new operational dimension. While the core concept of adjustments (in minus / in plus) remains unchanged for VAT purposes, the way they are documented, the timing of recognition, and formal requirements are significantly transformed.
Corrective invoices in KSeF
Once a taxpayer becomes subject to KSeF:
- every corrective invoice must be issued as a structured e-invoice,
- the document legally exists only once a KSeF number is assigned,
- the correction is automatically made available to the recipient in the system – there is no need to “deliver” it separately.
This represents a fundamental shift from the PDF/paper model, where delivery to the counterparty was essential.
“In minus” corrections
In KSeF:
- issue date = submission to KSeF,
- receipt date = assignment of the KSeF number.
This has a direct impact on VAT settlements, particularly for downward adjustments.
The issuer reduces the taxable base in the period in which the corrective invoice is issued in KSeF. This eliminates the previous requirement under Article 29a(13) of the VAT Act to hold documentation confirming that the conditions for the adjustment were agreed and met with the purchaser. This requirement remains relevant only for transactions not invoiced through KSeF.
“In plus” corrections
For upward adjustments:
- the standard rule applies – recognition either on a current basis or retroactively, depending on the cause,
- KSeF ensures a full audit trail (issue date, document identification, links to original invoices).
Formal requirements for corrective invoices in KSeF
A corrective invoice must include, among others:
- the KSeF number of the original invoice (if issued in the system),
- data identifying the original invoice,
- the reason for the correction,
- the scope of changes (amounts before and after correction).
In practice, this requires:
- integration of accounting systems with KSeF,
- proper data mapping and consistency.
Collective and technical corrections
KSeF allows for:
- collective corrections (e.g. retrospective rebates),
- technical corrections (e.g. formal errors).
In both cases, accurate linkage to original invoices is critical, which in a structured system requires precise and consistent data.
Corrections of invoices issued outside KSeF
This is one of the most important practical aspects for 2026.
The regulations explicitly allow – and in practice require – issuing corrections in KSeF for invoices originally issued before the system became mandatory.
Key principles:
- once a taxpayer is subject to KSeF, all corrective invoices must be issued within the system,
- this also applies to original invoices from 2025 and earlier (PDF/paper),
- the absence of a KSeF number for the original invoice does not prevent issuing a correction.
When issuing such a correction:
1. Include the original invoice data (date and number) in the “DaneFaKorygowanej” section,
2. Set the “NrKSeFN” field to 1, indicating that the original invoice was issued outside KSeF.
The legal basis is Article 106ga(1) of the VAT Act, which covers all corrections issued after KSeF becomes mandatory.
Key risks
The implementation of KSeF in the area of corrections involves several risks:
- incorrect linkage between the correction and the original invoice,
- improper determination of the VAT recognition period,
- inconsistencies between commercial documentation and invoicing data,
- system integration issues (ERP vs KSeF),
- failure to address “historical” corrections.
Summary
KSeF does not change the essence of corrective invoices, but it fundamentally reshapes their operational and technical handling. Of particular importance is the obligation to issue corrections in the system also for historical invoices, which in practice requires companies to organize and validate their data and processes ahead of full KSeF implementation.
For many businesses, the main challenge will not be the technology itself, but ensuring consistency between the actual transaction flow and the data reported within the system.
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