myDATA and Mandatory E-Invoicing: What Really Changes in 2025–2026

myDATA remains the backbone of digital tax reporting in Greece, but the important 2026 change is no longer just “future planning”. Mandatory electronic invoicing has now entered the legal framework through AADE decisions, and the rollout is phased. That point matters because many older articles present a single deadline for all businesses, which is no longer accurate.

What the mandatory e-invoicing framework covers

Under the current AADE decisions, mandatory electronic invoicing extends to:

• Domestic B2B wholesale transactions
• B2B transactions with entities in third countries outside the EU
• B2G transactions with General Government entities

The practical implication is that this is not just a myDATA classification issue. It changes how certain invoices must be issued in the first place.

The rollout is phased, not one-date-for-all

• First period: entities with gross revenue above €1,000,000 based on the 2023 income-tax return.
• The original launch for the first period was set for 2 February 2026, but AADE decision A.1044/2026 moved that start to 2 March 2026.
• For the first period, AADE also allowed a transition window until 3 May 2026, subject to the conditions of the decision and timely declaration.
• Second period: the next phase starts on 1 October 2026 under the framework of A.1128/2025.

Provider or timologio: what is actually available

The current framework does not mean that every business must necessarily contract a private provider in every case. The legal channels include:

• Certified e-invoicing providers
• The AADE timologio application

That is a major correction to many online summaries. A provider may still be the right operational choice for businesses with volume or ERP complexity, but the legal framework is more specific than “all companies must use a provider”.

Official incentives for early adoption

AADE decision A.1129/2025 activates the incentives of article 71TH of the Income Tax Code for entities that move to exclusive electronic invoicing before their mandatory start date. In practice, the framework provides an additional 100% tax uplift for the initial equipment or software cost and a corresponding uplift for invoice issuance, transmission and electronic archiving costs during the first 12 months.

Penalties: avoid generic tables

AADE issued E.2004/2026 to clarify how non-compliance is treated. The key point is that the sanction depends on the exact infringement and the applicable bookkeeping rule. That is why generic internet tables such as “€X per document” are not safe enough to use as a compliance map without checking the legal basis of the actual workflow.

What businesses should do now

1. Determine your phase using your 2023 gross revenue and document type mix.
2. Choose the correct channel: provider or timologio, based on legal scope and operational needs.
3. Submit the required declaration on time if you are using the transitional route.
4. Test issuance, MARK handling and archive flows before go-live.
5. Reconcile invoicing, myDATA, VAT and customer processes together instead of treating them as separate back-office tasks.

Apostolou & Partners helps businesses map their mandatory e-invoicing phase, choose the right implementation route and align invoicing with tax compliance. Contact us if you want a myDATA and e-invoicing readiness review.