Key figures — as of 2026-08-20: IRS payment deadline for 2025 income — 31 August 2026 — applies to anyone who filed on time between 1 April and 30 June — Finanças must issue the tax assessment (nota de liquidação) by 31 July — non-resident rental income (Category F) is taxed at a flat 28% with no progressive scale — late payment triggers daily juros compensatórios (compensatory interest) from the missed deadline.
The date that matters this week
If you own a rented flat, an Algarve villa let out on Airbnb, or any Portuguese-source income as a non-resident, 31 August is the day Finanças expects to be paid — or to have already paid you. For tax returns filed electronically by the legal deadline of 30 June, the Portuguese tax authorities issue the tax assessment by 31 July, and any tax due is payable by 31 August. Refunds work on the same clock: the Autoridade Tributária generally has until the end of August to complete the refund and payment cycle for returns filed within the normal campaign window.
For most PAYE employees this is a non-event handled automatically. For foreign owners of Portuguese property, it's often the one moment in the year when a real bill lands — because rental income, unlike a salary, usually isn't withheld at source in a way that matches the final tax owed.
Why non-resident landlords are exposed
Portugal taxes rental income under Category F, and the rules diverge sharply depending on residency. Since non-residents are only taxed on income sourced within Portugal, rental earnings from properties located in the country are subject to a flat tax rate of 28%, regardless of whether the rental is short term or long term. Crucially, non-residents cannot combine their rental income with other income sources, meaning they are subject to the fixed rate without any flexibility — there's no lower-bracket relief available the way there is for Portuguese tax residents.
That flat rate did shift for some resident landlords this year. The 2026 State Budget introduced a 10% rate for residential leases under the moderate rent regime — rent up to 2,300 euros per month and a contract of at least three years, but this concession is aimed at long-term residential lets, not short-term tourist rentals, and it's the resident regime, not the non-resident one. Non-residential lettings — commercial, industrial, services and agricultural land — stay at 28%, with no reduction regardless of rent level. A common and costly mistake, as one Portuguese tax adviser put it, is "Short-term letting is business income" being wrongly filed under the wrong category altogether — an error that resurfaces at the worst possible moment.
Non-residents aren't left with zero deductions, though: they can claim deductions on their rental income for maintenance and management costs, IMI property tax, and other related expenses, which is worth checking against your Modelo 3 annexes before assuming the worst.
GrowIN's calculation: what a typical Airbnb owner might owe
Take a non-resident who lets a Porto apartment short-term and nets €1,500 a month in rental profit after allowable deductions — €18,000 for the year. At the flat 28% Category F rate, that's a €5,040 tax bill for 2025 income, payable in full by 31 August 2026, with no option to spread it across lower brackets the way a resident could. That single number is why this deadline catches out more foreign owners than any other date on the Portuguese tax calendar — it's rarely covered by withholding, and it arrives as one lump sum rather than monthly deductions.
"For foreign landlords, 31 August isn't a formality — it's the one Finanças deadline with a real euro figure attached, and it comes due in full," says GrowIN Portugal Editorial.
What happens if you miss it
Missing the date doesn't mean immediate penalties, but it isn't free either. Compensatory interest (juros compensatórios) is charged on any IRS tax due that was paid late, accruing from the original payment due date of 31 August until the tax is actually paid. The rate itself moves with the Euribor and a statutory margin set by the AT, so it's worth checking the current published figure rather than assuming a fixed number — it's set by reference to the Euribor and a statutory margin published periodically by the AT, though taxpayers should generally expect a rate in the low single digits per year. If the sum owed is large and genuinely unaffordable in one go, taxpayers who are not financially able to pay within the time period can apply to pay by instalments in simplified form, provided they meet the conditions — worth raising with Finanças or an accountant before the deadline, not after.
Practical steps before 31 August
Log into the Portal das Finanças and check your nota de liquidação — if a payment is due, the document will show the exact amount and the Multibanco reference. Confirm your rental income was filed under the correct annex (Category F for long lets, business income for short-term Alojamento Local), and that deductible expenses — IMI, condominium fees, maintenance — were properly invoiced. If you're relying on a fiscal representative or accountant, this is the week to chase them rather than assume it's handled.
For anyone still getting to grips with how Portuguese property income interacts with residency status, our tax & NIF hub walks through NIF requirements, fiscal representation rules, and the IRS filing calendar in more depth. GrowIN's tax team can also review a rental-income filing before the deadline if you're unsure whether the right rate or annex was applied.
The window closes at the end of this month — after that, it's interest, not options, that starts accumulating.