myDATA 2026: a preparation checklist for accountants.

01The dates, and who they apply to

Two phases, both tied to the mandate that requires certain Greek-established sellers to issue invoices electronically:

02What actually becomes mandatory

The mandate obliges Greek-established sellers to issue certain invoices electronically, through a certified provider or AADE's own free tools (timologio or myDATAapp), covering domestic B2B sales, B2B exports to non-EU buyers, and B2G contracts. Domestic B2C retail sales are explicitly excluded and continue on normal receipt or invoice methods.

Two details matter for how a practice reads this: recipient consent is waived, a Greek buyer cannot opt out of receiving an e-invoice, and the obligation sits on the issuer, not the recipient. Pileform is not an e-invoicing provider and does not issue, transmit, or report e-invoices to myDATA, that role belongs to a certified provider or AADE's own tools; what a document-processing step like ours does is read what still arrives outside that channel.

03What stays outside myDATA regardless

The mandate is narrower than it sounds. It attaches to sellers established in Greece, so a few categories of document keep arriving exactly as before, on paper, PDF, or email, whatever a practice does about the mandate itself:

• Foreign supplier invoices. A supplier not established in Greece is outside the Greek mandate entirely, permanently, not just during a transitional window.
• B2C receipts. Domestic retail and consumer sales are explicitly excluded from the issuance obligation.
• The phase-1-to-phase-2 gap. Until 1 October 2026, and through the transitional window beyond it, a large population of smaller Greek suppliers is not yet obligated at all.
• Non-invoice documents. Bank statements, contracts, and delivery notes sit outside the structured e-invoice scope entirely.

None of that paper processes itself just because the mandate exists; it still needs reading, VAT applied per line, and posting, the same as it always did.

04A preparation checklist

Five things worth confirming per client before the next deadline:

• Confirm which phase each client falls into , using FY2023 gross revenue against the €1,000,000 threshold, not current-year turnover.
• Check whether a client has filed its declaration of use , either for a certified provider or for AADE's own timologio or myDATAapp tools.
• Note the penalty exposure for missed issuance , a flat fine plus a percentage of VAT due that escalates on repeat non-compliance, so late issuance is not a minor administrative slip.
• Keep processing foreign invoices and B2C receipts as before , since neither category is touched by this mandate, whatever else changes for a client's domestic B2B sales.
• Watch for further date movement , since the phase-1 start date has already slipped once; re-check AADE's own notices as each deadline approaches rather than assuming the current dates are final.