Frequently asked questions
Straight answers to the most common questions about self-billing and about ARQTA.
What is self-billing?
It is the regime set out in art. 36.º do CIVA (the Portuguese VAT Code) under which the invoice is issued by the buyer (whoever purchases the service) in the name and on behalf of the supplier. It is used when a company pays many service providers and wants every transaction invoiced uniformly and on time.
What is the prior self-billing agreement?
It is the legal authorisation that the supplier registers in the Portal das Finanças, giving the buyer’s NIF and the start date. Without this agreement, AT refuses to register the series and to accept the invoices. Each supplier registers the agreement only once; ARQTA sends them a step-by-step guide and checks automatically when it becomes active.
What is the ATCUD?
It is the unique document code required by Portaria n.º 195/2020, made up of the series’ validation code (assigned by AT when the series is registered) and the document’s sequential number. ARQTA registers the series by webservice and prints the ATCUD on every invoice and credit note.
Does the software need to be certified by AT?
Yes. Invoicing programs used by companies with organised accounts (contabilidade organizada) must be certified under Portaria n.º 363/2010, which includes the RSA signature chain, the statement «Processado por programa certificado» and compliance tests with AT. ARQTA is going through certification (see the Certification page).
Do suppliers need to create an ARQTA account?
No. The supplier only registers the prior agreement in their own Portal das Finanças account, following the guide they receive by e-mail. They share no passwords and create no sub-users.
How are VAT and withholding tax handled?
Each document applies a VAT rate (standard, intermediate or reduced, by tax region: Mainland, Azores or Madeira) or an exemption with the mandatory reason code. Withholding tax (IRS) is calculated on the taxable base, never on the VAT. In self-billing with prior agreement (com acordo), the withholding shown on the invoice is for information only; in self-billing without agreement (sem acordo) there is no withholding, because the activities it covers are supplies of goods.
Does ARQTA report the invoices to AT?
Yes: every document is reported to e-Fatura through the official webservice, and the SAF-T (PT) export is available per supplier, validated against the official schema of Portaria n.º 302/2016.
What happens if a supplier’s agreement is not active yet?
Payments can wait in a queue: the moment AT confirms the agreement, ARQTA registers the series and automatically issues the waiting invoices, in the right order.