There is a rule for IVA deadlines, and there is a published calendar. For one quarter in 2026 they disagree, and the calendar is the one you are held to.
The rule
CIVA art. 41 n.º 1 b) says a period is filed by day 20 of the second month after it ends, and the payment follows on day 25. Apply that to April–June and you get 20 August. That is the rule most summaries stop at, and for this one quarter it is the wrong answer.
What AT actually publishes
| Period | File by | Pay by |
|---|---|---|
| Q4 2025 | 20 February | 25 February |
| Q1 2026 | 20 May | 25 May |
| Q2 2026 | 21 September | 25 September |
| Q3 2026 | 20 November | 25 November |
Monthly filers
Monthly filing is mandatory once prior-year turnover reaches €650,000, and optional below it. The rhythm is the same: file by day 20 of the second following month, pay by day 25.
The deadline before the deadline
Invoice data goes to e-fatura by day 5 of the following month. It is easy to treat this as administrative, but the IVA return is reconciled against it, so a month that was never communicated becomes a return that cannot be substantiated.
When is the Q2 2026 IVA return due in Portugal?
21 September 2026 for filing and 25 September 2026 for payment. CIVA art. 41 n.º 1 b) would give 20 August, but the article under-determines this period: AT publishes 21 September in the Agenda Fiscal and that is the date taxpayers are held to. Do not derive it from the Code.
Is IVA filed monthly or quarterly in Portugal?
Quarterly by default. Monthly filing is mandatory once prior-year turnover reaches €650,000, and can also be opted into voluntarily.
When must invoices be reported to e-fatura?
By day 5 of the month following the month the invoices were issued.