Greece's Mandatory B2B E-invoicing: What Every Remaining Business Should Prepare For

Greece is moving decisively toward mandatory business-to-business (B2B) electronic invoicing, bringing the country into line with the wider European move toward real-time transaction reporting. The reform is being introduced on a phased basis and is expected to reach the remaining, smaller in-scope businesses in the later phase of the roll-out, closing off any escape route based on turnover. The framework rests on ministerial and Independent Authority for Public Revenue (AADE) decisions that set the timetable, the revenue threshold rule and the requirement that every electronic invoice be transmitted to the myDATA platform and assigned a MARK before delivery.

For finance directors, in-house tax teams, ERP owners and foreign groups with Greek subsidiaries, the window to act is narrow: a limited parallel-use period is provided, and only for businesses that have filed a valid declaration of start on time. This guide explains who is caught, which transactions are in scope, how the myDATA MARK process works, how to choose between the free AADE timologio and a certified provider, and the practical steps to complete before the transitional period ends.

Important: the precise phase dates, revenue thresholds and parallel-use windows are set by AADE and the Ministry of National Economy and Finance and have been subject to change and postponement. Businesses should confirm the current dates and thresholds directly against the latest AADE guidance and the relevant published decisions before acting.

Quick timeline (confirm current dates with AADE)

• First phase. Larger entities, those above a revenue threshold set by AADE (measured against a specified prior-year income tax return), become bound to issue B2B invoices electronically first.
• Close of the first-phase parallel-use window. A limited transitional period applies to the first wave of in-scope taxpayers before mandatory-only electronic issuance takes effect for them.
• Later phase. The remaining in-scope businesses below the first-phase threshold must issue B2B invoices via a certified provider or the AADE timologio.
• Close of the general parallel-use window. Steady-state, mandatory-only electronic issuance applies thereafter.

Who must comply in the later phase

The reform phases obligations by size. In the first phase, businesses above a revenue threshold set by AADE, measured against a specified prior-year income tax return, are bound to issue B2B invoices electronically first. The later phase then sweeps in every other in-scope taxpayer. In that phase, the remaining businesses that fall below the first-phase revenue threshold must issue their business-to-business invoices electronically, whether through a certified e-invoicing provider or the AADE timologio application.

The practical significance of this second phase is that it removes any remaining escape route based on turnover. Where the first wave captures larger enterprises with the resources and systems to adapt quickly, the later phase reaches the long tail of small and medium-sized businesses, professional firms and lower-volume issuers. Greece’s mandatory B2B e-invoicing affects every business in this category that was previously outside the threshold, meaning the compliance population expands significantly.

Entities in scope

The obligation applies broadly to taxable persons established in Greece that issue invoices for business-to-business transactions. In practical terms this includes:

• Legal entities. Companies of all corporate forms issuing invoices to other businesses for goods and services.
• Sole traders and professionals. Self-employed individuals and freelancers who invoice business customers.
• Branches and establishments. Greek establishments of businesses that generate domestic B2B invoicing obligations.

Because the phase dates are fixed once confirmed, entities should check their status against their revenue history now rather than waiting to be prompted. Businesses that were close to the applicable revenue threshold should verify which phase applies to them, since an incorrect assumption about the applicable date can leave a business exposed at go-live.

Exceptions

Not every sale is caught. The scope of the mandate excludes certain categories, most importantly:

• Retail B2C sales. Sales to final consumers are not part of the mandatory B2B e-invoicing obligation.
• Sales to other EU member states. Intra-EU B2B supplies to customers established in other member states fall outside the domestic mandate as currently specified.

These exclusions matter for scoping. A business that trades mainly with consumers or predominantly with EU counterparties will still have obligations for its domestic B2B flows, but the volume of transactions requiring electronic issuance may be smaller than a first glance suggests. Careful transaction-type mapping is essential before selecting a solution.

Which transactions are caught, domestic B2B, non-EU B2B and public contracts

The core of the mandate covers domestic business-to-business transactions. When a Greek business issues an invoice to another business established in Greece, that invoice must be issued electronically, transmitted to myDATA and assigned a MARK. Alongside domestic B2B, the framework is designed to align private-sector obligations with the state’s own e-invoicing requirements for public contracts and general government expenditure, and to address invoicing to non-EU business customers.

Equally important is what is excluded. Retail B2C sales to final consumers are outside the mandatory B2B scope, as are intra-EU B2B supplies to customers in other member states where the framework specifies their exclusion. Exports remain subject to their own VAT treatment. Greece’s mandatory B2B e-invoicing changes every domestic B2B invoicing workflow, but leaves consumer-facing and cross-border EU flows to be handled under their existing rules, which is why accurate categorisation of each transaction stream is a prerequisite for compliance.

Examples and common transaction scenarios

• Domestic wholesale supply. A Greek manufacturer invoices a Greek retailer for stock, in scope, electronic issuance with MARK required.
• Professional services to a company. A consultancy invoices a Greek corporate client for advisory work, in scope, electronic issuance required.
• Retail sale to a consumer. A shop issues a receipt to a walk-in customer, out of scope of the B2B mandate.
• Supply to a Germany-based business. A Greek exporter invoices a German company for an intra-EU supply, excluded from the domestic B2B mandate as currently specified.

These scenarios illustrate why a single business can face different treatment across its invoice book. A business that sells both to consumers and to other companies will need a solution capable of routing only the in-scope documents through the mandatory electronic channel while continuing to handle excluded transactions appropriately.

VAT and withholding implications when transmitting via myDATA

Because each in-scope invoice is transmitted to myDATA and assigned a MARK, the platform becomes a central record of the transaction for tax reporting purposes. The MARK links the issued document to the government’s data set, which in turn feeds the taxpayer’s declarations. Where withholding applies, the invoice data captured by myDATA supports the corresponding reporting. Businesses should ensure that VAT categorisation, rates and any withholding fields are correctly populated at the point of issue, because the electronic record transmitted through myDATA carries evidential weight and inconsistencies will be visible to the tax administration.

How myDATA, the MARK and transmission work

At the heart of the reform is transmission of invoice data to AADE. Every mandatory B2B invoice must be sent to the AADE myDATA platform, which assigns a unique registration number, the MARK (Μοναδικός Αριθμός Καταχώρησης), that must be present before the invoice is delivered to the customer. The process flow is straightforward in principle: the issuer generates the invoice, transmits it to myDATA (directly, via the timologio application, or through a certified provider acting on the issuer’s behalf), receives the MARK, and then delivers the completed, MARK-bearing document to the recipient.

The MARK is what gives the electronic invoice its legal and evidential standing. Without a MARK, the document is not a validly issued electronic invoice under the framework. This is why the choice of issuing channel, timologio or certified provider, is ultimately a question of how a business wants to connect to myDATA reliably and at the volume it requires, rather than whether it connects at all.

Data fields required

Each transmitted document must carry the data fields myDATA expects to identify the parties, the transaction, the tax treatment and the value. At a high level, issuers should expect to provide issuer and recipient identifiers, invoice type and series, issue date, line-item detail, VAT categorisation and amounts, and totals. The precise technical schema and accepted formats are set out in AADE’s myDATA technical documentation, and businesses, particularly those integrating an ERP, should map their internal invoice fields to the platform’s expected structure during implementation and testing.

Retention and audit trail obligations

Electronic issuance does not remove record-keeping duties; it reshapes them. Issued invoices, their MARKs and the associated transmission records form part of the audit trail that must be retained and made available on inspection, in line with the record-keeping requirements of the Greek Accounting Standards. Businesses should ensure their solution, whether timologio or a provider, preserves a complete, retrievable record of each transmitted document and its MARK, and that internal reconciliation between accounting systems and myDATA data is maintained so that the two never diverge.

Timologio versus certified e-invoicing providers, comparison and how to choose

Every business in scope must decide how it will issue electronically: through the AADE timologio, the tax authority’s free application, or through a certified e-invoicing provider. There is no single correct answer; the right choice depends on transaction volume, whether the business needs ERP integration, how many entities are involved, the level of support and service assurance required, and cost. The comparison below sets out the main decision criteria.

When timologio is the right choice

The timologio application is well suited to businesses with modest B2B invoice volumes, straightforward transaction types and no pressing need to integrate issuance into a larger ERP or finance system. Its principal advantages are that it is free and provided directly by AADE, removing any procurement step and any dependency on a third party’s certification. For a sole trader, a small professional firm or a low-volume company, timologio can deliver compliance quickly and at no licence cost.

The trade-offs are equally clear. Timologio offers limited integration and basic templates, and it is designed around manual or lightly automated issuance rather than high-throughput, multi-entity operations. Businesses that outgrow it, or that need custom fields and workflow automation, will find its constraints limiting. For those users, Greece’s mandatory B2B e-invoicing turns every issuance decision into a straightforward cost-versus-capability calculation, and timologio wins where volume and complexity are low.

When a certified provider is the right choice

A certified e-invoicing provider is the natural choice for medium and high-volume businesses, multi-entity groups and any organisation that needs invoicing to flow directly from its ERP. Providers offer full API integration, batch and automated transmission, custom field mapping, workflow controls and a commercial service level agreement with dedicated support. For foreign groups aligning several Greek subsidiaries, a provider that supports multi-jurisdictional flows can materially simplify governance.

The essential caveat is certification. Any provider must be AADE-certified, and a business should request and retain evidence of that certification before committing. Beyond certification, procurement should test security, availability, error handling, data-retention arrangements and the contractual allocation of liability for failed or delayed transmission. Because the provider transmits to myDATA on the issuer’s behalf, the issuer remains responsible for compliance and must be satisfied that the provider’s process reliably secures a MARK for every document.

How to declare the start of electronic issuance, process and deadlines

Access to any transitional parallel-use period is conditional on a declaration of start of electronic issuance. To benefit from parallel use, a business must file this declaration in time, with a start date no later than the applicable mandatory go-live date for its phase. In practice this means the declaration is not a formality to be left until go-live day; it is the gateway that preserves the right to run legacy and electronic methods side by side during the transitional window. Businesses already using timologio or a certified provider should confirm their declared start position rather than assume it is in place.

Sample declaration checklist

When preparing to declare, businesses should as a practical matter assemble:

• Taxpayer identification. The issuer’s tax registration details and entity information.
• Chosen issuing channel. Whether issuance will be via timologio or a named certified provider.
• Declared start date. A start date no later than the applicable mandatory go-live date to preserve parallel-use rights.
• Supporting evidence. Where a certified provider is used, retained proof of the provider’s AADE certification.

What to do if you missed the declaration deadline

A business that fails to file the declaration in time, or that declares a start date later than its mandatory go-live date, risks losing access to the parallel-use accommodation. The practical consequence is that it must move directly to compliant electronic issuance without the cushion of a transition period, and it may face enforcement exposure for any non-compliant invoicing in the interim. The recommended course is to file the declaration promptly, regularise the issuing method, and document the rectification steps taken. Because Greece’s mandatory B2B e-invoicing changes issuing obligations on fixed dates, the safest position is to treat the declaration as a priority action well ahead of go-live.

The parallel-use window, practical limits and transitional rules

A transitional parallel-use window is provided for each phase, but only for businesses that filed a valid declaration in time with a start date no later than their mandatory go-live date. During this period, a qualifying business may continue certain legacy issuance methods alongside compliant electronic issuance while systems, testing and staff readiness are finalised. These accommodations are time-limited by design and not open-ended, so businesses should confirm the exact opening and closing dates of the applicable window against current AADE guidance.

Systems and reconciliations during parallel use

The parallel period is an opportunity to prove the electronic process end to end, not a reason to delay it. Businesses should run their new issuing channel in earnest, reconcile every electronic document and its MARK against internal accounting records, and identify and fix any gaps before the window closes. Once the transitional latitude ends, mandatory-only electronic issuance applies, so any process weakness that survives the parallel period will surface as a live compliance problem. Treating the window as a controlled cut-over, rather than a grace period, is the difference between a smooth transition and a disruptive one.

Testing, certification and technical checks, IT and finance action plan

Technical readiness is where implementation succeeds or fails. Before go-live, businesses should test the full lifecycle of electronic issuance against myDATA, using representative sample data and confirming that documents transmit, receive a MARK and return to the system correctly. Testing should cover not only clean issuance but the exception paths that real operations generate.

What to test

• Standard issuance. Confirm an invoice transmits and receives a MARK, and that the MARK-bearing document is deliverable to the customer.
• Cancellations. Verify that cancellation flows are handled and reflected correctly.
• Credit notes and corrections. Test credit notes and corrective documents against the same transmission and MARK process.
• Error handling and fallback. Confirm behaviour when transmission fails, including retry logic and any fallback procedure, so no in-scope invoice is delivered without a MARK.

Who to involve

Successful testing is a shared responsibility. The finance team owns the transaction types, tax categorisation and reconciliation logic; the ERP vendor or internal IT owns the integration and data mapping; and, where used, the certified provider owns the transmission layer to myDATA. Roles should be agreed in writing, with a named owner for each test scenario and a clear go-live decision point. Building in enough lead time to test, fix and re-test before go-live is essential, because Greece’s mandatory B2B e-invoicing changes many issuers’ technical dependencies at once and support demand rises as the date approaches.

Contracts, supplier and customer terms, and audit readiness

Electronic issuance touches commercial agreements as well as systems. Supplier and customer contracts should be reviewed so that the mechanics of electronic invoicing, how invoices are delivered, when they are treated as accepted, and how corrections and returns are handled, are reflected in the terms. Where a certified provider transmits invoices on a party’s behalf, liability for failed or delayed transmission should be addressed. Retention, format and audit-readiness obligations should also be documented so that each party knows how records will be preserved and produced.

Sample contract clause prompts

• Delivery and acceptance. Define when an electronic invoice bearing a MARK is deemed delivered and accepted.
• Transmission liability. Allocate responsibility for failed or delayed transmission to myDATA.
• Corrections and returns. Set out the process for credit notes, cancellations and returns under electronic issuance.
• Retention and audit. Specify retention periods, formats and cooperation on inspections.

Action checklist for finance directors, foreign groups and advisers

With fixed dates once confirmed, sequencing matters. The plan below assigns owners and indicative deadlines so that the declaration, technical testing and contract updates all complete before the applicable parallel-use window closes. Align each deadline to the current dates confirmed with AADE.

For foreign groups, the same plan should be coordinated centrally across Greek subsidiaries so that channel selection, provider certification and contract updates are consistent. Qualified advisers with dedicated Greek tax practices can assist with scoping, provider selection and declarations.

Cross-border and EU alignment, how the reform affects a group’s approach

Greece’s reform sits within a broader European shift toward e-invoicing and real-time reporting, and that direction of travel matters for multinational groups. While the Greek mandate targets domestic B2B and excludes intra-EU B2B supplies to other member states as currently specified, groups operating across several jurisdictions increasingly face a patchwork of national mandates on different timetables. The practical effect for a foreign group is that Greece becomes one node in a wider compliance map, and the systems and providers chosen for Greek issuance should be assessed for their ability to support other member-state requirements as they come into force.

Aligning the Greek roll-out with the group’s wider e-invoicing strategy, rather than treating it in isolation, reduces duplicated effort and positions the group for the next mandate.

Conclusion and next steps

Greece’s mandatory B2B e-invoicing will reach every remaining in-scope business as the roll-out completes, and the transitional parallel-use windows are available only to those who file a valid declaration of start on time. The essential actions are clear: confirm which phase applies and the current dates with AADE, choose between the AADE timologio and a certified provider, file the declaration with a start date no later than the mandatory go-live, complete end-to-end testing against myDATA, and update contracts and internal procedures before the window closes. Businesses and foreign groups that treat this as a controlled cut-over rather than a last-minute obligation will move forward compliant and confident.

Tailored advice on scoping, provider selection, declarations and cross-border alignment is available for organisations that need it.

Sources

1. AADE (Independent Authority for Public Revenue), myDATA official guidance and technical documentation
2. National Printing House / Official Government Gazette (FEK), relevant ministerial and AADE decisions on mandatory B2B e-invoicing (verify current decision numbers and publication references)
3. AADE myDATA portal
4. Law 4308/2014 (Greek Accounting Standards), record-keeping and invoicing provisions