AT-Certified Invoicing Software in Portugal: What the Certification Requires

The first time I looked up what "AT certified" actually means for invoicing software in Portugal, I expected a feature checklist. What I found was a technical integration requirement: a live webservice connection to the tax authority's systems, a unique identifier assigned to every document, and a structured audit file maintained for inspection. Understanding those three things is the foundation of invoicing compliance in Portugal.

The requirement is set out in Portaria 363/2010 and applies to every invoicing software platform operating in Portugal, without exception.

What the certification involves

ATCUD codes. Every invoice, fatura-recibo, and Recibo Verde issued in Portugal must carry an ATCUD code. This is a unique document identifier generated by communicating with the AT webservice at the time of document creation. The code encodes a validation series (a string assigned specifically to your certified software and your NIF) plus a sequential document counter.

Without the AT webservice connection, there is no ATCUD. Without an ATCUD, the invoice does not exist in the Portuguese tax system. It is a valid-looking file, not a valid invoice.

QR codes. The QR code on every Portuguese invoice encodes the ATCUD along with the seller's NIF, the buyer's NIF where applicable, the document date, the taxable base, the VAT amount, and a hash of the document data. Scan it and you get an AT-hosted verification page for that specific document.

If the software is not certified, the QR code links to nothing. The document was never communicated to AT, so AT has no record to return.

SAF-T audit files. Certified software maintains a SAF-T (Standard Audit File for Tax) export of your complete invoicing activity. This is the structured XML record the AT uses in a tax inspection. It covers every document: invoices, credit notes, receipts, and any corrections. Annual SAF-T accounting file submission is on a separate timeline; the first mandatory filing for 2026 activity is due in 2028 under current rules.

The AT portal alternative

Before evaluating any software, it is worth noting that the AT portal itself is certified. The Portal das Finanças lets you issue Recibos Verdes (invoice-receipts) directly for free, and the portal handles ATCUD assignment and AT communication automatically.

For freelancers with a modest invoice volume, the portal is often the right choice. There is nothing to set up, no subscription, and the compliance mechanics are identical. Dedicated invoicing software adds value at higher volume, when you have recurring clients whose details you want to store, when invoicing foreign clients in other currencies, or when you want VAT and Social Security calculations visible alongside your invoicing activity.

For a full comparison of certified options across the market, see invoicing software for freelancers in Portugal: options and trade-offs.

Electronic signatures in 2026

A requirement that was creating confusion: qualified electronic signatures (QES) on invoices. A 2024 rule stated that PDF invoices would require a digital certificate from 1 January 2026. That deadline was postponed.

Under Lei 73-A/2025 (Orçamento de Estado 2026), the QES requirement on PDF invoices now applies from 1 January 2027. In 2026, ATCUD plus QR code is the full requirement for a fiscally valid PDF invoice. No digital certificate is needed this year. The full picture on PDF invoices and QES in 2026 and 2027 covers the postponement and what it means in practice.

Verifying certification

Certified software providers list their AT certificate number in their documentation. You can verify any number against the AT's public registry on Portal das Finanças under "Softwares de Faturação Certificados." If a tool does not list a certificate number, it is not certified.

One other decision that comes up when setting up invoicing in Portugal: which document type to issue. The choice between a fatura and a Recibo Verde comes down to your activity type and what your client needs from the document. That is a separate decision from software choice, and the answer is usually the same regardless of which certified platform you use.

The certification question is the first thing to verify. After that, the choice between tools comes down to workflow and which additional obligations you want the software to handle beyond the invoicing layer.