If you invoice anything in Greece, your invoice data goes to the tax authority. Not once a year with your tax return, but as you issue each invoice. The platform that collects it is called myDATA. Most freelancers never log in, but it shapes what AADE sees when it checks your returns.
The short answer
- What it is: AADE’s electronic books platform. The name stands for “my Digital Accounting and Tax Application” (AADE).
- What goes in: the data of every invoice and receipt you issue, plus the classification of your expenses.
- Who sends it: your invoicing tool does it when you issue the invoice. Expense classification is usually your accountant’s job.
- MARK: every valid transmission gets a unique registration number from AADE.
- Timing: invoices are reported in real time when issued through a provider, timologio or ERP software. Expenses are classified by your VAT return deadline.
- E-invoicing is separate: from 2 November 2026 some invoices must also be issued through approved channels. That builds on myDATA, it doesn’t replace it.
What myDATA actually is
myDATA is a database at AADE that holds a digital copy of your books. The legal basis is Article 16 of the Tax Procedure Code (Law 5104/2024): every business must transmit the data of the accounting documents it issues to AADE electronically, regardless of how they were issued. The details (what, how, when) are set by AADE decision A.1138/2020, amended several times since (codified text, AADE).
AADE presents it as the basis for automated tax returns. In practice, AADE knows your invoiced income before you file anything.
What has to be reported
Your income: every invoice and receipt
Every invoice or receipt you issue has to reach myDATA. This includes:
- invoices to Greek clients,
- invoices to businesses in other EU countries,
- invoices to clients outside the EU,
- receipts to private customers.
The client’s location matters for VAT and for e-invoicing, but not for myDATA. A developer billing only a German company still reports every invoice. How the VAT side works is covered in VAT for freelancers with foreign clients.
Your expenses: classification
Your suppliers report the invoices they issue to you. Those invoices then appear in your myDATA account and have to be classified: what kind of expense is it, and how does it count for VAT and income tax. In practice your accountant does this.
If a Greek supplier didn’t report an invoice, or reported a lower amount than the real one, the obligation shifts to you: as the recipient, you report the omission before the VAT return deadline for that period (A.1138/2020, art. 5).
Who transmits: the channels
The main ways to get data into myDATA (AADE):
- Certified e-invoicing provider. A private company approved by AADE. Your invoice is transmitted as it is issued.
- ERP or accounting software connected to myDATA.
- AADE’s free timologio app (web) or myDATAapp (mobile). For a freelancer with a few invoices a month this is usually enough. See our guide to timologio.
- The special registration form on the myDATA site, open only to small businesses within set limits on revenue and number of invoices.
- Cash registers (fiscal devices) for retail businesses, which report receipts automatically.
An invoice typed in Word and emailed as a PDF has not been reported.
The MARK number
Every valid transmission receives a MARK (Μοναδικός Αριθμός Καταχώρησης), the unique registration number AADE assigns (A.1138/2020, art. 1). Invoices issued through timologio also carry a QR code that links to the document in myDATA.
A MARK is your proof that the invoice reached AADE.
Timing
Under A.1138/2020 as currently in force (taxheaven overview):
| What | When |
|---|---|
| Invoices via provider, timologio or ERP | Real time, when issued |
| Invoices via the special form | By the day after issue |
| Classification of expense invoices from Greek suppliers | By the VAT return deadline for the period |
| Recipient reporting a supplier’s missing or understated invoice | Before the VAT return deadline |
| Payroll entries | With the withholding tax return |
| Depreciation and year-end adjusting entries | With the income tax return |
myDATA has no single annual deadline. It runs alongside your VAT return cycle, monthly or quarterly. For all dates in one place, see the Greek tax deadlines calendar.
myDATA and e-invoicing: how they fit together
myDATA is where invoice data ends up. E-invoicing regulates how certain invoices are issued.
From 2 November 2026, freelancers and businesses with revenue up to €1 million (per their 2023 tax return) must issue invoices to Greek businesses and businesses outside the EU through an approved provider or timologio/myDATAapp (AADE decision A.1197/2026). Invoices to the public sector (B2G) have had to be electronic since 1 September 2025 under separate rules (Lawspot). Until 31 January 2027, a transition period lets you keep using other channels alongside. It only applies if you declared your e-invoicing method (provider or timologio) in time, with a start date no later than 2 November 2026. Invoices to EU businesses and private customers are outside the mandate but still go to myDATA.
Who is in scope, declarations and penalties: e-invoicing in Greece explained.
Common mistakes
Invoices that never reached myDATA. Usually a self-made PDF, or software that isn’t actually connected. Under Article 16(2), AADE cannot assess your income lower than what myDATA shows. Unreported invoices don’t make income disappear; they create a gap between your books and AADE’s.
Expenses you can’t deduct. The same article says expenses are not deductible if their documents were not transmitted electronically. A supplier invoice missing from myDATA is a cost you may lose, unless you report the omission in time.
Mismatches between myDATA, your books and your bank. Invoices cancelled on paper but not in myDATA, credit notes issued as new invoices, duplicate transmissions. Each one is a discrepancy AADE can see.
Wrong treatment of foreign clients. An invoice to an EU business carries no Greek VAT under reverse charge but still needs the right VAT exemption category in myDATA, and usually a VIES statement.
What it costs to get wrong
An invoice that should have been issued electronically but wasn’t counts as an invoice not issued at all. For invoices with VAT, a first offence costs 50% of the VAT, with a minimum of €250 (single-entry books) or €500 (double-entry books); without VAT, €500 or €1,000 per audit (Tax Procedure Code art. 57). Repeat offences cost more.
Invoices that were issued but never transmitted fall under Article 58 of the Tax Procedure Code: 10% of the net value of each missing invoice, capped at €250 per day, and half that if the data arrives late. Missing payroll, depreciation or year-end entries cost €250 (single-entry books) or €500 (double-entry books) per year and breach. These fines only apply from a start date the Finance Minister still has to set by decision. As of November 2026, they are law but not yet enforced.
The less visible cost is the gap itself: income AADE counts and expenses it won’t accept.
Getting it under control
For most freelancers, myDATA takes little effort once the setup is right: one invoicing channel that transmits everything, an accountant who classifies expenses before each VAT return, and a regular check that myDATA matches your books. If your current accountant doesn’t do that, switching takes about a week.
At taxomade, myDATA is part of our ongoing bookkeeping from €89/month, all inclusive: we classify your expenses, prepare and file your VAT returns and annual return, and check that myDATA matches your books. Message us on WhatsApp for a free compliance check. For the bigger tax picture, see freelancer taxes in Greece.
Frequently asked questions
What is myDATA in Greece?
myDATA (my Digital Accounting and Tax Application) is the electronic books platform of the Greek tax authority AADE. Businesses and freelancers report the data of every invoice they issue, and their expense classifications, to it. AADE uses this data to cross-check tax returns.
Do I have to report every invoice to myDATA?
Yes. Every invoice or receipt you issue has to be transmitted to myDATA, whatever tool you use to issue it. Each valid transmission receives a MARK, a unique registration number assigned by AADE.
Do invoices to foreign clients have to be reported to myDATA?
Yes. Invoices to clients in other EU countries, outside the EU and to private customers all have to be reported. The client’s location changes the VAT treatment and whether the e-invoicing mandate applies, not the myDATA obligation.
What is the difference between myDATA and e-invoicing?
myDATA is the reporting platform where invoice data reaches AADE. E-invoicing regulates how certain invoices are issued: from 2 November 2026, invoices to Greek businesses and businesses outside the EU must be issued through an approved provider or AADE’s free timologio or myDATAapp (public-sector invoices since 1 September 2025).
Who classifies expenses in myDATA, me or my accountant?
In practice your accountant. Expense invoices from Greek suppliers are classified by the deadline of the VAT return for the period. Payroll entries follow the withholding tax return, and depreciation and other year-end entries follow the income tax return.
What happens if an invoice is missing from myDATA?
AADE cannot assess your income lower than what myDATA shows, and expenses whose documents were not transmitted are not deductible. If a supplier fails to report an invoice, you as the recipient report the omission before your VAT return deadline.
Rules as of November 2026 (Tax Procedure Code, Law 5104/2024, art. 16, 57 and 58, A.1138/2020 as amended, A.1128/2025 as amended by A.1197/2026).