KSeF gives tax authorities access to detailed invoice data in near-real time. KAS analytical systems can automatically compare sales invoices at one taxpayer with cost invoices at another, detect discrepancies against JPK_VAT and JPK_CIT, and identify related-party transactions. For CFOs this means one thing: record consistency is no longer optional. Every invoice is now directly accessible to the authority — with date, amount and counterparty.
Does this apply to your company
This article applies to you if you meet at least one condition:
- You are an active VAT taxpayer — from 1 February or 1 April 2026 you issue invoices through KSeF
- You conduct related-party transactions — KSeF identifies them automatically by tax ID
- You have historical discrepancies between VAT records and CIT records
- You apply special cost recognition rules (limited-deductibility costs, non-deductible costs, intragroup intangible services)
- Your sector is typically targeted by KAS inspections (construction, IT, high-value goods trading, intragroup intangible services)
What the authority sees — 4 data areas
| Data available in KSeF | What KAS can automatically check |
|---|---|
| Every VAT invoice with issuer and recipient tax ID, date, amount, VAT rate | Comparing the sales invoice at the supplier with the cost invoice at the buyer — detecting unreported invoices |
| Invoice date and KSeF number assignment date | Verifying timely VAT reporting — whether the invoice was included in JPK_V7 in the correct period |
| Tax ID of all counterparties on every transaction | Automatic identification of ownership links and related-party transactions |
| Invoice values per counterparty per period | Detecting anomalies: sudden transaction volume changes, unknown counterparties, mutual invoice corrections |
KSeF as a KAS analytics tool — how it works
Before KSeF the tax authority had data from JPK_VAT — a list of invoices in a file submitted after each month end. These were retrospective data, selectively analysed by the authorities.
KSeF changes this fundamentally. Every invoice is available to the Ministry of Finance at the moment of issuance — before the VAT return is filed. This means the KAS analytics system can:
- Compare company A's sales invoices with company B's cost invoices before both file JPK_V7
- Identify invoices issued in KSeF that were not included in the taxpayer's JPK_VAT
- Detect "duplicate" or "cancelled" invoices outside KSeF
- Build taxpayer transaction profiles with data going back several years
How to prepare your company — auditor's perspective
Step 1 — Reconcile historical JPK_VAT records against KSeF data
Before KSeF goes live it is worth conducting an internal review of the last 3 years: are all cost invoices you claimed as input VAT present at the counterparty? Discrepancies discovered now can be explained or corrected. Discrepancies discovered by the tax authority are grounds for initiating an audit.
Step 2 — Document cost classification rules
Under JPK_CIT every entry must have a deductible/non-deductible marker. The tax classification decision must be documented and approved — not made ad hoc by the bookkeeper. The tax advisor or CFO must approve the rules for each cost category.
Step 3 — Review transfer pricing documentation
KSeF automatically identifies related-party transactions. If your transfer pricing documentation is out of date or incomplete — KSeF will give KAS the full transaction volume picture, increasing the probability of a transfer pricing audit.
Step 4 — Verify credit notes
Credit notes (upward and downward adjustments) must be included in VAT records in the correct period. In KSeF every credit note has its own number and date — the KAS system sees credit notes and compares them against both parties' returns.
High-risk areas after KSeF implementation
- Unbooked or delayed cost invoices — the counterparty issued the invoice in KSeF but you did not book it in the same period. The authority sees the gap.
- Invoices "outside KSeF" — if the company issued any invoices outside the mandatory system (e.g. in offline mode not in compliance with the rules), KAS will detect this by comparing data.
- VAT rate discrepancies — the issuer applied a 23% rate, the recipient deducted VAT at 8%. Immediately visible inconsistency in KSeF.
- Related-party transactions at non-market prices — KSeF gives the authority transaction volumes; comparison against a market benchmark is the next verification step.
- Selective cost invoice recognition — the company selects which cost invoices to recognise as deductible. In KSeF all invoices are visible, so selective recognition requires documented justification.
Frequently asked questions
What to do before KSeF goes live
- Conduct an internal review of the last 2–3 years — are there any cost invoices not included in JPK_VAT or booked with a delay?
- Review transfer pricing documentation — is it current for related-party transactions that will now be fully visible in KSeF?
- Document cost classification rules (deductible/non-deductible) — each cost category should have a written rule approved by the CFO or tax advisor.
- Review credit notes from the last 3 years — are they recognised in the correct period on both sides of the transaction?
- Consult your auditor and tax advisor — a pre-implementation risk assessment is cheaper than explanations after an audit.
Want to discuss how this topic applies to your company?
Book a short consultation with a statutory auditor and assess which risks or actions may apply to your situation.