e-Invoicing in Portugal: Timeline, Guidelines, Process, and Steps for Implementation

Portugal is moving towards full digitalisation of its invoicing system, covering both B2G and B2B transactions. Large enterprises have already implemented structured e-invoicing for B2G transactions. However, small and medium-sized enterprises (SMEs) now have until January 1, 2026, to comply with B2G e-invoicing mandates, until then, they may issue PDF invoices with a qualified electronic signature. 

While B2B e-invoicing remains optional, businesses must maintain a strict audit trail to meet  Autoridade Tributária e Aduaneira (AT), the tax authority requirements. Portugal follows the CIUS-PT framework under the PEPPOL BIS 3.0 format, based on a clearance model. This guide breaks down Portugal’s e-invoicing regulations, key deadlines, and how businesses can prepare for a smooth transition.

What is e-Invoicing in Portugal?

Portugal's e-invoicing is an electronic invoicing system for issuing, receiving, and storing invoices in digital form. Portugal requires e-invoices in CIUS-PT format (UBL 2.1 or CEFACT) to be signed electronically via a Qualified Electronic Signature (QES). Companies are required to utilize AT-certified software when creating invoices that must be created with core transaction data, QR code and ATCUD (Unique Document Code). For B2G, invoices are issued through the FE-AP platform or any other specified software; for B2B, any channel providing end-to-end SAF-T audit functionality is acceptable, with QES being required from 1 January 2026. All invoices need to be retained electronically for 10 years to comply with Autoridade Tributária e Aduaneira (AT) requirements.

e-Invoice Implementation Timeline

Portugal has been gradually following e-invoicing implementation with key deadlines for different business categories.

*SAF-T (Standard Audit File for Tax) is a standardised electronic format for accounting and tax data.

e-Invoicing Process in Portugal

Portugal's e-invoicing system mandates structured electronic invoices for B2G transactions and introduces stricter compliance rules for B2B from 2026. Here is a step-by-step procedure: 

1. Generate the Invoice: Businesses have to use AT-certified invoicing software. Make sure the invoice is in the CIUS-PT format (UBL 2.1 or CEFACT). Include all mandatory details: invoice number, tax identification, billing period, payment terms, and transaction details. Use a Qualified Electronic Signature (QES) for legal validity. 
2. Obtain ATCUD and QR Code (If Applicable): You can use an AT-certified software to generate the Unique Document Code (ATCUD). Further, the QR code is mandatory for paper invoices and PDFs.
3. Transmitting Invoices For B2G (Business-to-Government): Send through the FE-AP platform (via WebServices or AS2). If not listed on FE-AP, contact the specific public entity to confirm transmission requirements. Alternatively you can use third-party portals, direct EDI connection, or email.
4. Transmitting Invoices For B2B (Business-to-Business): Businesses can use EDI, direct transmission, or any system ensuring a complete business audit trail. From January 1, 2026, a Qualified Electronic Signature (QES) will also be required.
5. Receiving & Validating the e-invoice: Invoices must be received in CIUS-PT format for B2G transactions. Businesses can validate invoice details using ERP or invoicing software. Public entities may use FE-AP or their own validation platforms

e-Invoicing Compliance Guidelines

These key points are crucial to ensure compliance with e-invoice guidelines in Portugal:

• All government sector suppliers are required to issue invoices in CIUS-PT format (UBL 2.1 or CEFACT).
• SMEs are allowed to retain PDF as e-invoices in Portugal until December 31, 2025.
• From January 1, 2026, invoices should be accompanied by a Qualified Electronic Signature (QES).
• Invoices should have the ATCUD (Unique Document Code) and a QR Code, which should be generated by AT-certified software.
• Invoices B2G should be sent through the FE-AP platform, direct EDI, or email (according to the public entity).
• Both the parties should store e-invoices for 10 years.

Who Needs to Comply with e-Invoicing in Portugal?

Portuguese companies are required to adhere to e-invoicing in Portugal based on size and type of transactions.

• Large companies: Mandatory B2G e-invoicing since 2021.
• Public sector suppliers: Must issue invoices in CIUS-PT format.
• SMEs & micro-enterprises: B2G e-invoicing mandatory from January 1, 2026.
• B2B transactions: Not mandatory, but QR codes & ATCUD required on PDFs.
• All businesses: Must use AT-certified software and comply with SAF-T reporting.

Benefits of e-Invoicing in Portugal

Here are the multiple benefits of Portugal e-invoicing: 

• Compliance: Guarantees tax compliance with Portuguese tax regulations and reduces penalties.
• Cost savings: Saves on paper invoices, printing, and storage expenses.
• Faster processing: Simplifies invoice verification, approval, and payment.
• Improved security: Minimizes fraud risk with QES and AT-certified applications.
• Improved tax control: Facilitates auditing and tax reporting with SAF-T files.

How can ClearTax help a business with e-Invoicing in Portugal?

ClearTax, a reliable e-invoicing solutions provider, enables businesses to comply with Portugal's e-invoicing law through:

• Seamless Integration with ERP & POS: Automates invoice creation and sending in CIUS-PT format to the public administration. 
• Real-Time Compliance Validation: Validates invoices according to Portuguese tax authority (AT) and VAT legislation.
• Cloud-Based e-invoicing Platform: Facilitates easy tracking, reconciling, and handling invoices.
• Automated Reporting & Compliance Alerts: Minimizes errors, deadline lapses, and non-compliance risks.

Government Resources

Here are a few government resources to help you better understand the e-invoicing process in Portugal: 

1. Tax Authority-  Autoridade Tributária e Aduaneira (AT)
2. 2025 Budget Law
3. List of Public Entities Reachable via the FE-AP portal
4. CIUS-PT Format Specifications 
5. E-invoicing homepage & resources on the eSPap website

Conclusion

Portugal requires e-invoicing for B2G, with large companies already under the requirement, and SMEs are given until January 1, 2026. B2B e-invoicing is optional but must adhere to strict tax authority (AT) regulations, such as QR codes and Qualified Electronic Signatures (QES). The adoption of the CIUS-PT format and ensuring proper transmission via certified platforms is obligatory for businesses. ClearTax makes compliance easy by automating invoice creation, real-time validation, smooth ERP integration, and error-free reporting, enabling businesses to easily comply.