Short answer: KSeF, Poland's national e-invoicing system, has been mandatory since 1 February 2026 for the largest taxpayers and since 1 April 2026 for most other businesses. From 1 January 2027 it also covers the smallest ones — those with sales up to PLN 10,000 gross a month. Receiving invoices through KSeF has applied to practically everyone since February. Until the end of 2026 the Ministry of Finance is not imposing financial penalties for errors, but from 1 January 2027 that grace period ends.
I am writing this in early October, when most of my clients are "in the system" but typically on minimal settings: sales invoices go out, while purchase invoices are still retyped into accounting by hand. This guide is the pillar of my KSeF articles — it gathers deadlines, risks and an action plan, and I cover individual topics in separate posts.
This is a practitioner's IT guide, not tax advice. Please confirm how the rules apply to you with your accountant or tax adviser.
KSeF timeline — who is covered and when
| Date | Who | What changes |
|---|---|---|
| 1 Feb 2026 | Taxpayers with 2024 sales above PLN 200m | Mandatory issuing of invoices in KSeF |
| 1 Feb 2026 | All taxpayers | Invoices can (and must be able to) be received from KSeF |
| 1 Apr 2026 | Remaining businesses (apart from the smallest) | Mandatory structured invoices |
| 1 Jan 2027 | Businesses with sales up to PLN 10,000 gross a month | Exemption ends, full obligation |
| 1 Jan 2027 | Everyone | Financial penalties begin |
Two things clients regularly confuse:
- The obligation covers B2B invoices. Sales to consumers (B2C) can still be documented with a receipt or an invoice outside KSeF — but each sales model should be checked individually.
- "Small taxpayer" does not mean "small company". The exemption until the end of 2026 only applied to those within the PLN 10,000 gross monthly sales limit. A company with a few employees and PLN 80,000 turnover came in from April.
Penalties from 2027 — what is actually at stake
Until the end of 2026, financial penalties for late or incorrect issuing are not applied. From 1 January 2027, sanctions can reach up to 100% of the VAT shown on the invoice, or up to 18.7% of the gross value where there is no VAT. They apply, among other things, to:
- issuing an invoice outside KSeF without entitlement,
- failing to submit on time an invoice issued in offline or outage mode,
- issuing a non-compliant invoice during such a period.
Fiscal criminal law runs independently and has no transition period. That is why I treat 2026 as time to tidy up the process, not as "a year without consequences".
Fallback modes: offline, offline24 and system outage
The most common question I hear: "What if KSeF is down, or I have no internet?" You have three routes:
| Mode | When | What you do |
|---|---|---|
| Offline24 | Any time, your choice | Issue the invoice in your software, give it to the buyer (QR code), submit to KSeF by the next business day |
| Offline | Failure on your side or no connectivity | Issue outside KSeF and submit once the problem is fixed, within the set deadline |
| KSeF outage | Ministry announces a system failure | Issue outside KSeF and submit after the outage ends |
What I see in practice: the biggest problem is not the procedure itself but that nobody in the company knows who is responsible for submitting the invoices afterwards. An offline24 invoice sits on a salesperson's laptop and reaches KSeF late — and from 2027 those are precisely the cases that will be penalised.
Access to KSeF: tokens, certificates and permissions
KSeF has no single username and password for everything. Invoicing software connects via a token or a KSeF certificate, and permissions are granted to people and systems (issuing, viewing, granting access). That is good news for security — provided you do it sensibly.
The most common mistakes in my experience:
- One token for the whole company, stored in an email or on a sticky note. When someone leaves, nobody knows what to revoke.
- Full permissions for everybody "so that it works".
- No process owner — the accountant assumes the company watches purchase invoices, the company assumes the accountancy firm does.
If access worries you, note that this is the same kind of hygiene required by the NIS2 directive — I covered it in NIS2 for small and medium businesses in 2026.
KSeF rollout plan — 6 steps
This is the order I follow with clients. For a company with one or two people handling invoices, the whole thing usually takes a few days to two weeks.
- Inventory. Which software do you issue invoices from? Does it have a ready KSeF integration? Who issues them and who books costs? The answers take an hour and save weeks.
- Update or change the software. Most popular systems have an integration. Older boxed versions can be a problem — then switching tools is cheaper than patching.
- Access set-up. Named permissions, a separate token or certificate for the system, written rules for revoking access when someone leaves.
- Fallback procedure. One A4 page: who does what, and by when, in offline mode. Printed, not just "somewhere in the cloud".
- Purchase invoice handling. The most neglected element. Supplier invoices now land in KSeF, not in your mailbox — someone has to fetch, approve and pass them to accounting.
- Live test. Issue a few real invoices, check the KSeF number, the status and what the buyer sees.
Roughly, based on my quotes: configuring KSeF in software you already have is typically PLN 500–1,500 (about £110–330). Automatic fetching of invoices, approval and hand-off to accounting is usually PLN 3,000–8,000 (£660–1,760). A full ERP integration plus OCR for documents outside KSeF runs PLN 8,000–20,000 (£1,760–4,400). These are ranges, not an offer; I always give an exact price after a conversation.
Where KSeF really eats time — purchase invoices
Issuing is simple in KSeF because the software does it. The real change is on the purchasing side. Before KSeF became mandatory, a supplier's invoice arrived by email as a PDF. Today its "original" is an XML file in KSeF, and the PDF is only a visualisation.
An example scenario: a service company with 80 purchase invoices a month. If someone logs in to KSeF manually, downloads, describes and forwards them to the accountant, that realistically takes 5–8 hours a month, plus the risk of an invoice going astray. An automation (n8n, Make) does it without human involvement: it fetches new invoices, extracts the data, sends them for approval under a rule such as "amount above X → owner", and passes them on to accounting. A person just clicks "approve". I describe the details on the KSeF and invoice workflow automation page, and general automation principles in AI automation for small businesses.
Who is responsible for what: company, accountant, software vendor
Before you roll anything out, write down the division of roles — it takes a quarter of an hour and saves arguments later. This split works for my clients: the company is responsible for issuing invoices and submitting them on time in fallback modes, the accountant for settling purchase invoices once approved, and the software vendor for keeping the KSeF integration working after every update. The fourth role people forget is a deputy for the process owner during holidays. Once those four names are on paper, half of the KSeF problems disappear before they appear.
The most common mistakes I see
- Leaving everything to the last minute. The bottleneck is not technology but the availability of the accountant and the software vendor at year end.
- Assuming the accountancy firm "will do KSeF for us". The firm can have permissions, but you remain responsible for invoices issued and received.
- No procedure for foreign invoices and receipts. Not everything goes through KSeF — invoices from foreign suppliers or tickets need a separate path (OCR).
- Ignoring outage notices. You need to be able to read them and know what to do about them.
- One person as the bottleneck. When all KSeF knowledge sits in one head, a holiday means penalty risk.
FAQ
Does every company have to use KSeF in 2026?
Receiving invoices through KSeF applies to practically everyone from February 2026. Issuing is mandatory from April 2026, except for businesses with sales up to PLN 10,000 gross a month, which join in January 2027. Some sales, such as those to consumers, are also outside the scope.
Are there penalties for KSeF errors right now?
Financial sanctions for late or incorrect issuing are not applied until the end of 2026. Fiscal criminal liability works independently, though, and from 1 January 2027 penalties can reach 100% of the invoice VAT or 18.7% of the gross value.
What should I do when KSeF is down?
Issue the invoice in offline or outage mode, give it to the buyer and submit it to KSeF within the required deadline. The key is to decide in advance who is responsible for this.
Will my accountancy firm handle my KSeF invoices?
It can be granted permissions to fetch and view invoices, but responsibility for correct issuing and timely submission stays with you. It is worth agreeing this in writing.
How much does a KSeF rollout cost a small company?
Configuring your existing software is roughly PLN 500–1,500. Automating purchase invoices is usually PLN 3,000–8,000, and a full ERP integration costs more. It depends on invoice volume and the systems in use.
Summary
KSeF is no longer "someday" — it is reality, and 2027 brings penalties and the smallest businesses. The sensible plan for the last quarter of 2026: tidy up access, write down the fallback procedure and automate purchase invoices, because that is where the most time leaks away.
If you would like to check where your company stands — especially if you are in Swarzędz, Kórnik or another town near Poznań and prefer to go through it with someone on site — write to me via the contact form. The first conversation is free.