Unique Document Code
ATCUD
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The English term for ATCUD, the unique identifier on every Portuguese invoice that lets anyone verify the document's authenticity with the tax authority.
The unique document code is the English way of referring to the ATCUD: the mandatory identifier that appears on every invoice, receipt, and fiscal document issued in Portugal.
If you've received an invoice from a Portuguese freelancer or company, you've seen it: a short alphanumeric code, usually near the top of the document, sitting above a QR code. Together, they let you verify the document is real.
What you're looking at
The code follows a simple format: a validation code, a hyphen, and a sequential number. For example, XKRF9821-15 means this is the 15th document in a series whose validation code is XKRF9821.
The validation code is assigned by the Portuguese tax authority (AT) when an invoicing system registers a document series. The sequential number counts upward with each document in that series. No two documents in Portugal will ever share the same ATCUD.
Why it matters
For Portuguese freelancers, the ATCUD is part of the compliance landscape. Certified invoicing software generates it automatically, there's nothing to configure or manage.
For clients and businesses receiving Portuguese invoices, the ATCUD is a verification tool. Scan the QR code that accompanies it, and you'll reach a tax authority page confirming whether the document is legitimate. This is useful when processing invoices from new suppliers or verifying documents during audits.
The broader system
Portugal has been steadily digitizing its tax system. The ATCUD is one piece of a larger framework:
- Certified invoicing software: all software that issues fiscal documents in Portugal must be certified by the tax authority and registered for ATCUD generation.
- Invoice series registration: before issuing documents, each series (invoices, invoice-receipts, credit notes) must be registered through the Portal das Finanças.
- QR codes: accompany every ATCUD, linking to the tax authority's verification system.
- SAF-T reporting: the standardized audit file format that ties all documents together for tax reporting.
The goal is a system where every fiscal document is traceable from creation to tax declaration, with no gaps.
For the technical format details and how the validation code is obtained, see the Portuguese entry: ATCUD.
Frequently asked questions
What is the unique document code on Portuguese invoices?
It's the ATCUD (AT Code Unique Document), a mandatory identifier on every invoice and receipt in Portugal. It combines a validation code from the tax authority with a sequential document number, formatted as 'ABCD1234-1'.
Why do Portuguese invoices have a unique code?
The ATCUD lets anyone verify that a document is genuine and was issued through certified software. It's part of Portugal's effort to digitize tax compliance and reduce fraud. Together with the QR code, it creates a verifiable chain from the document to the tax authority.
Do invoices from the Recibo Verde portal also have an ATCUD?
Yes. Documents issued through the Portal das Finanças (including Recibos Verdes) include an ATCUD. The portal is itself a certified system, so it generates the code automatically.
Can I check if an invoice's ATCUD is valid?
Yes. The QR code on the document links to a verification page on the tax authority's website. You can scan it to confirm the document is registered. The ATCUD itself is also verifiable through the Portal das Finanças.
What if I receive a Portuguese invoice without an ATCUD?
Since January 2023, all Portuguese invoices and receipts must include an ATCUD. A document without one may not have been issued through certified software, which could be a compliance issue. If you're a business receiving such an invoice, ask the issuer for a corrected document.
Related terms
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.
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.