Published 25 October 2026

The KSeF number in transfer titles from 2027 — what has to change in your system

From 1 January 2027 a transfer paying a KSeF invoice must carry its KSeF number. Here is who the obligation applies to, what the collective identifier is, and what to change in a system that creates its own transfers.

In short

From 1 January 2027, an active VAT payer paying another active VAT payer for an invoice issued in KSeF must include that invoice’s KSeF number in the payment. Paying several invoices in one transfer uses a collective identifier generated in KSeF. If your own system creates the transfers, it needs preparing for this.

What changes on 1 January 2027

The new Art. 108g of the Polish VAT Act applies to payments made from 1 January 2027. According to the Ministry of Finance, the obligation falls on a buyer who:

is an active VAT payer,
pays for a structured invoice (issued in KSeF) or for an invoice issued in offline mode (KSeF unavailability or offline24),
pays another active VAT payer,
pays by credit transfer or another payment instrument.

The obligation also covers third parties who make the payment. Where payment is made by direct debit, the obligation falls on the invoice issuer.

Paying one invoice — you give its KSeF number.
Paying several invoices at once — you give a collective identifier.

The KSeF number and the collective identifier

The KSeF number uniquely identifies an invoice in KSeF. KSeF returns it in the UPO (the official confirmation of receipt); it isn’t part of the invoice XML itself. A number KSeF issued for an invoice on the test environment looks like this:

1234563218-20260925-5177F4000005-FA (35 characters)

The collective identifier is an aggregate number for at least two invoices. It is generated in KSeF by declaring the list of the invoices’ KSeF numbers, and either the issuer or the recipient can generate it. It has 35 characters: the NIP of the authentication context, the marker “IZ” with the year and month, a unique 12-character string and two check characters. The Ministry’s documentation gives this example:

9999999999-IZ202602-FFFFFFFFFFFF-FF

Split payment (MPP)

The obligation also covers payments under the split-payment mechanism. The MPP transfer message carries, among other things, the invoice’s KSeF number. When paying several invoices, the collective identifier is given instead of the period the payment covers.

When the number isn’t required

The Ministry names an exception for invoices issued in offline mode (KSeF unavailability or offline24) that were not entered into KSeF because of an announced outage.

Questions about how far the obligation reaches in your company — for example card payments, offsets or prepayments — are best settled with your accountant or tax adviser. This article covers the technical side.

What this means for your system

If your own system prepares the transfers — an ERP, finance software or a bank-export script — then:

It must know the KSeF number of every invoice it pays. Purchase invoices (or at least their metadata, including the KSeF number) have to be fetched from KSeF and the number stored with the invoice.
Each transfer must be linked to an invoice. Every payable has to be matched to a specific KSeF invoice or set of invoices.
Paying several invoices needs a collective identifier, generated in KSeF from their numbers.
The number goes into the payment title — in the bank export file or the bank API call. Check the title-field length limit in your bank’s format: a KSeF number has 35 characters.
MPP uses its own message format — the KSeF number takes the place of the invoice number.
Exceptions need handling, e.g. offline invoices not entered into KSeF because of an announced outage.

Checklist

Does your system store the KSeF number with every purchase invoice?
Does your system create the transfers (export, bank API), or does someone enter them by hand?
Do you pay several invoices in one transfer? Then you need a collective identifier.
Do you pay under split payment (MPP)?
Will the changes be tested before 1 January 2027?

How I can help

With the 2027 package I prepare your system for this obligation: a review of how transfers are created, fetching purchase invoices’ KSeF numbers, the KSeF number or collective identifier in the transfer title, MPP handling, and testing on the KSeF test environment. Fixed price: PLN 3,900 net + 23% VAT.

Sources (in Polish)

This article is for information only and is not tax advice. The Polish version prevails. Status as of 25 October 2026.