When does KSeF become mandatory?

KSeF is already mandatory. From 1 February 2026 it covers taxpayers whose 2024 sales (including tax) exceeded 200M PLN, and from 1 April 2026 every remaining VAT payer — both active and exempt.

Do small businesses have to use KSeF too?

Yes. Small businesses and sole traders are covered from 1 April 2026. The one exception: the smallest sellers, whose monthly sales including tax stay at or below 10,000 PLN — for them the full obligation starts on 1 January 2027.

What happens if you don't issue an invoice in KSeF?

A B2B invoice issued outside KSeF is not a valid invoice under the law. Violations carry financial penalties — so it pays to roll out and test the system in the TEST environment first.

KSeF Mandatory in 2026: Deadlines, Thresholds, Who

KSeF is mandatory from 1 February 2026 for companies with sales above 200M PLN in 2024, and from 1 April 2026 for all other VAT payers (both active and exempt). The smallest sellers — at or below 10,000 PLN in monthly sales — aren't covered until 1 January 2027.

The National e-Invoicing System (KSeF) is already mandatory. A B2B invoice issued outside the system is not a valid invoice under the law — it must be created as a structured invoice in the FA(3) format and submitted to KSeF, which assigns it a unique number and issues an official confirmation of receipt (UPO).

The legal basis is the act of 5 August 2025 (Dz.U. 2025 item 1203), signed on 27 August 2025. This guide lays out who the obligation covers, when, and how to get ready.

When do you have to start issuing invoices in KSeF?

You must issue invoices in KSeF from 1 February 2026 (companies with sales over 200M PLN in 2024) and from 1 April 2026 (all other VAT payers). The smallest sellers (≤ 10,000 PLN/month) follow on 1 January 2027. The obligation rolled out in stages, by sales volume. The first two deadlines have already passed — KSeF applies now:

1 February 2026 — taxpayers whose sales (including tax) exceeded 200M PLN in 2024.
1 April 2026 — all remaining VAT payers, both active and exempt.
1 January 2027 — the smallest sellers, whose total monthly sales (including tax) are ≤ 10,000 PLN. Until then they can still issue electronic or paper invoices (art. 145m).

If you're not in the smallest group with the deferral to 2027, the obligation already applies to you.

Confirm the exact dates and thresholds against the current Ministry of Finance notice on gov.pl — we update this article as things change.

What "structured invoice" actually means

It's an invoice in a strictly defined XML format — FA(3) — instead of a PDF or paper. You don't issue it "by hand": your accounting system or invoicing tool builds the XML, signs the session, and sends the document to KSeF. In return you get a KSeF number and a UPO — proof that the invoice reached the system.

Who the obligation covers

B2B sales in Poland by a VAT payer based in PL — covered.
Export of services and goods, plus WDT (intra-EU supply) to businesses — also goes through KSeF, including at the 0% rate (more in the article on the export invoice).
B2C sales (consumer) — optional, outside the structured-invoice obligation.
Not covered: among others, the OSS/IOSS procedures and foreign entities with no seat or fixed place of business in Poland. So KSeF does not cover "every invoice."

How to prepare — a step-by-step checklist

Pin down your deadline — if your monthly sales exceed 10,000 PLN, the obligation already applies; smaller sellers have until 1 January 2027.
Connect to the TEST environment — KSeF 2.0 offers a test environment with fictional authorization; you can submit a trial invoice at no risk.
Automate issuing — if you sell through Stripe, invoices can flow into KSeF automatically once they're finalized in Stripe (see the Stripe + KSeF integration).
Practice corrections (KOR) — corrections go through KSeF too.
Move to PROD deliberately — only once the process works on TEST.

Common misconceptions

"KSeF is just another PDF" — no, it's structured XML with an official number.
"Emailing it is enough" — a B2B invoice outside KSeF no longer exists in law.
"I'll make it in the last week" — authorization, tokens, and testing take time; do it early.

Start with a free test

KSeF Kit lets you submit your first test invoice with no card and no commitment — straight from your Stripe invoices. See how submission works or run the system yourself.