ATCUD
Unique Document Code
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AT Code Unique Document: the unique identifier required on every invoice and receipt in Portugal, combining a validation code from the tax authority with a sequential number.
ATCUD stands for Código Único de Documento da AT, the unique document code that the Portuguese tax authority (AT) requires on every invoice, receipt, and fiscal document issued in Portugal.
How it works
Every ATCUD is made of two parts joined by a hyphen:
- Validation code: a code you get from the tax authority when you register an invoice series. Think of it as the series' fingerprint.
- Sequential number: the document's position within that series.
So an ATCUD like ABCD1234-7 means: this is document number 7 in the series identified by validation code ABCD1234.
Why it exists
Before ATCUD, verifying a Portuguese invoice required access to the tax authority's internal systems. Now, any document can be checked independently. The ATCUD, together with the QR code that accompanies it, lets the tax authority (or a client, or an auditor) confirm that a document is genuine and was issued by certified software.
This is part of Portugal's broader push toward digital tax compliance. Every invoice has a traceable identity from the moment it's created.
Registration of invoice series
Before you can issue documents with a valid ATCUD, your invoicing software must register each document series with the tax authority through the Portal das Finanças. The registration returns a validation code for that series. Each series, FT for invoices, FR for invoice-receipts, NC for credit notes, gets its own code.
Certified software handles this automatically. You don't need to visit the portal or manage codes manually.
Placement on documents
The ATCUD must appear on every page of a printed or PDF document, positioned above the QR code. The two work as a pair: the ATCUD is human-readable, the QR code is machine-readable. Together, they form a complete verification system.
What certified software does for you
If you're using certified invoicing software, you don't need to think about ATCUD at all. The software registers your series, obtains validation codes, assigns sequential numbers, and prints both the ATCUD and QR code on every document. It's fully automatic.
Frequently asked questions
What is an ATCUD?
ATCUD stands for AT Code Unique Document (Código Único de Documento da AT). It's a unique identifier that must appear on every invoice, receipt, and fiscal document issued in Portugal. It combines a validation code from the tax authority with a sequential number.
What does an ATCUD look like?
It follows the format 'ABCD1234-1' where the first part is the validation code obtained from the tax authority when you register an invoice series, and the number after the hyphen is the sequential document number within that series.
When did ATCUD become mandatory?
ATCUD became mandatory on all Portuguese invoices and receipts from January 2023. Before that date, it was optional. All certified invoicing software must now generate it automatically.
Where does the ATCUD appear on a document?
It must appear on every page of the printed or PDF document, positioned above the QR code. Both the ATCUD and QR code work together to allow the tax authority (or anyone) to verify the document's authenticity.
Do I need to generate the ATCUD myself?
No. If you use certified invoicing software, it handles ATCUD generation automatically. The software registers your invoice series with the tax authority, obtains the validation code, and combines it with the sequential number for each document you issue.
Related terms
The English term for ATCUD, the unique identifier on every Portuguese invoice that lets anyone verify the document's authenticity with the tax authority.
FaturaInvoiceA formal invoice issued through certified software or the AT portal. For solo entrepreneurs on the simplified regime, income tax and Social Security remain cash-basis (tied to payment) regardless of when the invoice is issued.
Fatura-ReciboInvoice-ReceiptA combined invoice and receipt document issued by Portuguese solo entrepreneurs when payment is received, the document type behind the Recibo Verde system.
Portal das FinançasTax Authority PortalThe Portuguese tax authority's online portal where freelancers issue Recibos Verdes, file tax declarations, register invoice series, and manage their tax obligations.