Key takeaways
- The Peppol five-corner model adds a fifth actor to the four-corner model: the tax authority.
- That fifth corner receives the transaction data: this is the architecture of continuous transaction controls (CTC).
- OpenPeppol has published a CTC reference document (first edition in September 2021, supplemented by an addendum in September 2023).
- In Belgium, the 2026 B2B mandate stays on the four-corner model; tax reporting belongs to a later stage, within the ViDA framework.
From the four-corner to the five-corner model of Peppol
The Peppol network was first designed for a clear goal: to route an invoice from one business to another in a structured, interoperable way. That architecture is the four-corner model. The Peppol five-corner model answers a different question: how to let a tax authority receive the data of an invoice without breaking the business exchange that already exists.
The shift is not theoretical. With the European ViDA package (VAT in the Digital Age), digital reporting of transactions becomes a concrete regulatory horizon for businesses across the Union. The fifth corner is the technical building block that links invoicing to tax control.
This article explains what the fifth corner adds, what continuous transaction controls cover, and where Belgium stands in this movement. For the four corners themselves, read The Peppol four-corner model; for the network as a whole, Understanding the Peppol network in 5 minutes.
What continuous transaction controls (CTC) cover
Continuous transaction controls, or CTC, are the mechanisms by which a tax authority obtains the data of a transaction at the moment it is issued, or shortly after, rather than during a later audit of documents already archived.
The change in logic runs deep. The traditional model is after-the-fact control: the business invoices, keeps its records, and the authority checks later. The CTC model brings control closer to the moment of the transaction. Depending on the country, this takes the form of electronic reporting (e-reporting) of the data, transmission of the invoice to the authority, or a prior validation step.
The forms CTC can take
Reporting of the data
The business reports the key invoice data to the authority continuously, rather than through a single periodic aggregate return.
Transmission of the invoice
A structured copy of the invoice is transmitted to the authority as part of the exchange.
Prior validation
In some regimes, the invoice goes through a control step before it is considered valid.
The fifth corner: the tax authority in the exchange
In the four-corner model, an invoice travels from the sender (corner 1) to their access point (corner 2), then to the recipient's access point (corner 3) and finally to the recipient (corner 4). The document stays a matter between two businesses and their providers.
The five-corner model keeps this path and adds a fifth corner: the tax authority, which receives the transaction data. The business exchange is not replaced; it is doubled with a flow toward control. The business keeps issuing and receiving its invoices as before, and the reporting runs over the same access-point infrastructure.
corners for the exchange
sender, sender's access point, recipient's access point, recipient
the fifth corner
the tax authority that receives the data
semantic foundation
the standard shared by the invoice and the reporting
This continuity is the main advantage of the Peppol approach: a business already connected to send its invoices does not have to deploy a second channel dedicated to the tax authority. It is the access point, and the shared semantic standard, that absorb the new role.
Four corners or five: who does what
The common confusion pits the two models against each other as if you had to choose. In reality, the five-corner model does not cancel the four-corner model: it stacks on top of it. The table places each role.
| Four-corner model | Five-corner model | |
|---|---|---|
| Routes the invoice from sender to recipient | ||
| Relies on Peppol access points | ||
| Transmits data to the tax authority | ||
| Serves continuous transaction controls (CTC) |
OpenPeppol has documented this CTC direction in a dedicated reference document. Its first edition dates from September 2021 and was supplemented by an addendum published in September 2023. These documents describe how the Peppol network can serve as the support for continuous-control regimes, preserving the interoperability that makes its value.
ViDA: why the fifth corner becomes a European issue
The five-corner model would remain a technical curiosity without the regulatory framework that makes it necessary. That framework is ViDA (VAT in the Digital Age), the European Union package modernising the VAT rules. Its centrepiece, Directive (EU) 2025/516, entered into force on 14 April 2025 and introduces digital reporting obligations based on e-invoicing and the EN 16931 standard.
For cross-border transactions between businesses, ViDA provides for near-real-time digital reporting anchored on the e-invoice, with a rollout scheduled across the Union. National real-time reporting systems will then have to converge toward this common model. That is exactly the kind of flow the fifth corner lets you organise. For the detailed calendar and stages, read ViDA: what the EU is preparing for VAT.
- 1
CTC reference document
September 2021OpenPeppol publishes the first edition of its reference document on continuous transaction controls.
- 2
CTC addendum
September 2023An addendum supplements the reference document with learnings from deployments.
- 3
ViDA enters into force
April 2025Directive (EU) 2025/516 enters into force and opens the way to digital reporting.
- 4
Belgian B2B mandate
January 2026Structured B2B e-invoicing through Peppol becomes mandatory (four-corner model).
Ready for e-invoicing, ready for what comes next
YouInv generates and sends your compliant Peppol invoices over the network, the base on which tomorrow's tax reporting will build.
Where Belgium stands
Here you have to avoid a calendar mistake. The Belgian B2B e-invoicing mandate on 1 January 2026 does not put the five-corner model in place. It mandates the exchange of structured invoices compliant with EN 16931, through Peppol, that is, the four-corner model. Nothing, at that date, is transmitted in real time to the tax authority.
The electronic reporting (e-reporting) component is announced as a separate, later stage, consistent with the European calendar carried by ViDA. In other words, Belgian businesses first adopt the four-corner exchange; the fifth corner will come afterward, on top of an infrastructure already in place. The order matters: connecting correctly today also means preparing for tomorrow's reporting. For how to connect, see Peppol access point: what it is for.
The good news is continuity. A business that becomes compliant to send and receive its invoices through Peppol is not building a throwaway system: it lays the base onto which tax reporting will graft. The criterion for choosing your tool does not change at its core: being able to generate, validate and transmit compliant documents through an access point.
What to remember is the direction of travel. The network that carries your invoices today is the same one that, tomorrow, will carry the data to the authority. Understanding the fifth corner means understanding why a good Peppol connection is an investment, not a box to tick.
Further reading
- The Peppol four-corner model: the base architecture of the exchange.
- ViDA: what the EU is preparing for VAT: the European framework for digital reporting.
- Peppol in Belgium: the B2B mandate on 1 January 2026: who is in scope and from when.
The reference source is authoritative: the OpenPeppol CTC documentation.
What is the Peppol five-corner model?
The five-corner model extends Peppol's four-corner model by adding a fifth actor: the tax authority. On top of the four existing corners (sender, sender's access point, recipient's access point, recipient), a fifth corner receives the transaction data for control purposes. This is the architecture behind continuous transaction controls (CTC).
What are continuous transaction controls (CTC)?
Continuous transaction controls, or CTC, are the mechanisms by which a tax authority obtains invoice data at or near the moment the invoice is issued, rather than during a later audit. Electronic reporting (e-reporting) and invoicing with transmission to the authority are forms of CTC.
What is the difference between the four-corner and five-corner models?
The four-corner model routes an invoice from the sender to the recipient through their respective access points. The five-corner model keeps that exchange and adds a transmission of the data to the tax authority, the fifth corner. One serves the business exchange, the other grafts tax control onto it.
Is the five-corner model mandatory in Belgium in 2026?
No. The Belgian B2B e-invoicing mandate on 1 January 2026 rests on exchanging structured invoices through Peppol, that is, the four-corner model, with no real-time transmission to the authority. An electronic reporting (e-reporting) component is announced for a later stage and fits within the EU ViDA framework.
How does the five-corner model relate to ViDA?
ViDA (VAT in the Digital Age) introduces digital reporting obligations for cross-border transactions, based on the EN 16931 standard and e-invoicing. The Peppol five-corner model is the technical architecture that lets you combine the invoice exchange with transmission of data to the authority, at the heart of this CTC logic.
