For many businesses, the phrase "electronic invoicing" sounds like yet another technical burden. In practice, however, it is not simply a change from paper to PDF. It is a change in the way an invoice is issued, transmitted, accepted and documented. It affects the accounting department, the ERP, sales, contracts with customers, the relationship with the accountant, the choice of provider and the day-to-day proof that the business complies.

2026 is pivotal because mandatory electronic invoicing is being implemented gradually. The large businesses of the first period started with a postponed timetable, while from autumn the remaining obliged entities follow. At the same time, myDATA remains the central mechanism of the electronic books of AADE, and the business must distinguish what "I issue an electronic invoice" means from "I transmit data to myDATA".

Do not leave it only to the accountant or only to the technician

Electronic invoicing is a business flow: sales, ERP, accounting, customers, provider, errors and documentation must work as one unified system.

This guide explains in plain language what changes, which dates a business should watch and what to organize in practice before the issue becomes urgent.

Desk with laptop, invoices and financial documents for electronic invoicing and myDATA
Electronic invoicing needs a shared flow between sales, ERP, accounting, provider and myDATA.

First clarification: electronic invoicing does not simply mean PDF

A PDF created in Word or sent by email is not, by itself, the solution for mandatory electronic invoicing. The point of the regulation is that there must be a specific way of issuance and transmission, with technical and tax traceability. AADE distinguishes methods such as the use of an Electronic Invoicing Services Provider or the use of the timologio application, while myDATA collects and records document summaries and classifications.

In simple terms:

ConceptWhat it means in practiceCommon mistake
Electronic invoiceAn invoice issued by an accepted electronic method for the transactions covered by the obligation"I sent a PDF, so I am fine"
myDATAAADE's electronic books platform where data is transmitted/recorded"Since it goes up to myDATA, issuance does not concern me"
Electronic invoicing providerA certified service that undertakes issuance and transmission through a specific procedure"The provider is only a technical cost"
ERP/accounting softwareThe program the business uses for sales, invoices, warehouse and customers"The accountant will fix it alone"
AADE timologioApplication for issuing and transmitting documents through AADE"It is suitable for every complex commercial flow"

The right question is not "which button do I press?". It is: what invoicing flow does my business have and which method legally and practically covers that flow?

Which transactions it concerns

Based on AADE decisions and the Greek Accounting Standards, the framework covers electronic invoice issuance in basic categories of transactions. Indicatively, it includes wholesale transactions within Greece to entities subject to the Greek Accounting Standards, wholesale transactions to foreign entities in third countries outside the EU, as well as transactions concerning public contracts or other expenditure of General Government bodies.

This means that a business should not only look at whether it "issues many invoices". It must look at whom it invoices, what types of transactions it has, whether there is B2G invoicing, whether it issues to businesses in Greece, whether it has exports to third countries and which systems are involved.

The key dates of 2026

Mandatory application is divided into two periods. The first concerns businesses with gross revenue exceeding EUR 1,000,000, based on the income tax return for tax year 2023 or, for special cases of legal persons, the tax year that started in 2023. The second concerns the remaining obliged entities.

Decision A.1044/2026 postponed the timetable for the first period. Thus, for businesses in the first period, the obligation starts from 2 March 2026, with a transitional possibility of gradual fulfillment until 3 May 2026, provided that the prescribed declarations of use/start have been made. For the second period, the basic date remains 1 October 2026, with a transitional period until 31 December 2026, under conditions.

PeriodWho it coversBasic startTransitional periodWhat the business should do
First periodObliged entities with gross revenue over EUR 1,000,000 based on tax year 202302/03/2026until 03/05/2026Check whether the declaration for using a provider or timologio has been submitted correctly and whether the flow actually works
Second periodRemaining obliged entities01/10/2026until 31/12/2026Choose solution, test ERP, train staff, agree with accounting department and customers

The transitional period should not be read as "postponement without obligations". It is time for adjustment under conditions. If a business waits until the last week, it will face technical settings, document series, user rights, customer fields, VAT, classifications and cancellation procedures that are not always solved in one day.

How it relates to myDATA

myDATA is AADE's digital platform for electronic books. There, summaries of revenue and expense documents are transmitted and recorded, transactions are classified and the necessary accounting entries for determining results are supported.

Electronic invoicing, however, mainly concerns the method of issuing the invoice. myDATA concerns the electronic transmission/recording of data. In practice, the two worlds are connected. If the business issues through a provider, transmission may happen automatically. If it uses ERP or another flow, it must be clear who sends what, when and with what responsibility.

The most common problem is not that the business has no program at all. It is that it has a program, accountant, commercial circuit, warehouse and e-shop, but nobody has defined who has final responsibility when something is rejected, sent incorrectly or not matched.

Provider, ERP or timologio: how do I decide?

There is no single solution for everyone. A small business with a few invoices per month may be covered differently from a trading company with warehouse, orders, branches, B2B customers, foreign transactions and public contracts.

Business profilePossible approachWhat to watch
Very small business with a few B2B invoicesConsider using timologio or a simple AADE-compatible solutionIt should not be so manual that it creates errors
Trading business with warehouse and many customersERP with proper integration or providerSeries, returns, credit notes, deliveries, customers, VAT
Business with B2G/Public sectorCompatibility with public-contract requirements and PEPPOL where neededDo not assume that a simple PDF is enough for the public sector
E-shop with B2B and B2C flowsConnection of e-shop, ERP, orders, payments and documentsOrders and invoices must not remain disconnected
Group or business with many issuing pointsCentral architecture and user rightsAudit trail, roles, avoiding duplicate issuance

The choice of solution must be made through a joint discussion between management, accountant, technical/ERP partner and, where needed, legal or tax adviser. The worst scenario is for the business to buy a solution without having mapped its flows.

What a business should check before application

The transition is easier when it is treated as a small compliance project and not as "install a plugin". A practical checklist is the following:

StepWhat we checkWho is involved
1. Inclusion and periodWhether the business is in the first or second period, based on revenue/activityAccounting department, management
2. Transaction typesB2B Greece, third countries, public sector, special flowsAccounting department, sales
3. Current issuanceWhere invoices are issued today and by which usersERP/IT, accounting department
4. Customers and detailsVAT number, addresses, VAT status, country, public bodiesSales, back office
5. Series and documentsInvoices, credit notes, cancellation documents, delivery notes, special casesAccountant, ERP
6. Transmission and errorsWho sees rejections, errors and non-matchesIT, accounting department
7. TrainingWho issues, who approves, who cancelsManagement, users
8. DocumentationPolicy, user instructions, proof of declarations/settingsManagement, accounting department

If a business has a large volume of invoices, testing must be done with real scenarios: advance payment, partial delivery, credit note, foreign customer, public body, wrong VAT number, series change, internet interruption, price change after issuance.

Fines and risk: why it is not only a technical issue

AADE has issued guidance on breaches of non-compliance with the electronic invoicing obligation. The business must understand that non-compliance may be treated as a tax violation and not as a simple technical inability. If it cannot prove that it applied the procedure correctly, the risk does not stay in the accounting department.

Beyond the fine, there is also operational risk: customers who do not accept an invoice, payment delays, wrong transmission, disagreements with accounting, blocked invoicing at month-end, mismatch with myDATA and additional support cost.

Good compliance is visible in three points:

  1. The business knows which obligation concerns it and from when.
  2. The issuance process works technically before the deadline.
  3. There is a person who monitors errors, rejections and corrections.

Example: small trading company

A trading company with turnover of EUR 650,000 in 2023 may belong to the second period. This does not mean it should wait until September 2026. If it has ERP, e-shop, salespeople issuing documents and warehouse, it must start earlier. It will need to see whether the ERP supports the flow, whether the accountant has access to errors, whether customers have correct details and whether the documents issued by the e-shop are matched correctly.

The critical point is not to press the first invoice on 1 October. The critical point is not to have invoicing stop on 3 October because nobody had tested a credit note or cancellation.

Example: company with revenue above EUR 1,000,000

For a company that belongs to the first period, the issue is more immediate. From 2 March 2026 the obligation has already been activated, with a transitional period until 3 May 2026 under conditions. If the company used the transitional possibility, it must have clear evidence that it submitted the required declarations on time and did not leave the adjustment only as an intention.

In such a company, management should request a status report: which flow is applied, which provider or application is used, how many documents were issued correctly, how many failed, which were corrected and which remain open.

What to write in an internal policy

A huge manual is not needed. What is needed, however, is a short practical text that says:

  • from which date the obligation applies to the business,
  • which issuance solution is used,
  • who has the right to issue and cancel,
  • who checks transmission errors,
  • how mistakes are corrected,
  • who informs the accountant,
  • where proof of settings, declarations and reports is kept.

This document also protects the business in practice. When an employee, accountant or technical partner changes, everything does not have to be discovered from the beginning.

Frequently asked questions

Does myDATA mean that I do not need electronic invoicing?

No. myDATA is the electronic books and data transmission/recording platform. Mandatory electronic invoicing concerns the way the invoice is issued for specific transactions and obliged entities. The two concepts are connected, but they are not the same.

Can I use only timologio?

It may be a solution for some businesses, especially where the flow is simple. But if there are complex sales, warehouse, many issuing points, e-shop or special flows, it must be carefully examined whether it covers the actual operation.

If I have ERP, am I automatically fine?

No. The ERP must be correctly configured, support the required flows and have an error-control procedure. The fact that a program has a "myDATA button" does not mean that the whole business is compliant.

What should I ask the accountant and the technician?

Ask for a written picture: which period you belong to, which solution is proposed, which declarations are needed, which tests were done, which errors appeared and who monitors them.

When should I start if I am in the second period?

Not at the last minute. The second period starts on 1 October 2026 and has a transitional margin until 31 December 2026 under conditions. Preparation, however, must start earlier, especially if there is ERP or a large number of documents.

Useful sources