Electronic Invoicing: What Changes from October 1, 2026

From October 1, 2026, the mandatory issuance of B2B documents through a certified e-invoicing provider (or the AADE API) extends to all Greek businesses, regardless of size and turnover; the data of each invoice is transmitted by the provider automatically to myDATA. The first phase, which began on February 2, 2026, applied only to businesses with a turnover above 1 million euros. From October, the obligation reaches small and medium-sized enterprises, self-employed professionals, and small commercial or craft businesses — in other words, the overwhelming majority of Greek businesses.

Three months is enough time to prepare properly, without last-minute pressure. It is not, however, enough time to let pass without a plan.

myDATA and electronic invoicing are not the same thing

myDATA is AADE's digital infrastructure where the data of every document automatically ends up. The obligation that changes on 1/10/2026 does not concern myDATA itself, but the way the invoice is issued: it must be issued through a certified e-invoicing provider or directly via the AADE API. myDATA is the recipient of the data that results automatically from this process — not a separate, parallel obligation.

What "electronic invoicing" means in practice

Electronic invoicing is not simply an invoice in a PDF file that you send by email. It is an invoice issued through a certified e-invoicing provider or directly via the AADE API, which receives a unique registration number (MARK) and is automatically transmitted to myDATA and to the counterparty. The plain paper or scanned invoice, even if it "gets by" today, will no longer meet the legal requirements for B2B transactions.

AADE's objective is twofold: the automatic pre-filling of tax returns and the reduction of tax evasion through full digital traceability of every transaction.

What you risk if you delay

Non-compliance is not merely an administrative omission — it carries a direct financial cost. AADE has announced fines ranging from 250 to 2,500 euros per violation, which can reach up to 50% of the VAT for each document found during an audit to have been unlawfully issued. For a business with a regular volume of invoices, this is not a theoretical risk; it is a cost that multiplies quickly.

The incentive worth knowing before you decide when to act

There is also a reason not to wait until the last week of September. Businesses that join the e-invoicing system before the mandatory start date that applies to them are entitled to an additional 100% tax deduction on expenses for the purchase of the necessary equipment and software, for a period of 12 months. In other words: timely adaptation is not treated by the state merely as an obligation — it is specifically rewarded. A business that moves in July or August, instead of September, has something tangible to gain.

Four practical steps to be ready before October

First, check your current accounting or invoicing software: does it already support integration with a certified e-invoicing provider? If not, this is your first decision point.

Second, choose a provider early. The market will be flooded with requests in September as the deadline approaches — moving early gives you time for testing and adjustment, rather than a rushed last-minute installation.

Third, consider whether early adoption makes sense for your business, so that you can claim the tax deduction incentive before the deadline for submitting the relevant application expires.

Fourth, inform your accounting department and everyone in the business who issues or manages documents in good time — the change affects the issuing process, not just the software.

You don't have to manage this on your own

The transition to electronic invoicing touches simultaneously on the accounting function, the choice of technology provider, and tax planning — three areas where MDC Stiakakis already supports businesses on a daily basis. If you would like us to assess your business's readiness together and plan the next steps before October 1, contact us.

This article intends to inform the reader and in no way substitutes the specialized consulting services. For more information, please contact MDC Stiakakis SA