Key figures — as of 2026-10-02: 20 October — deadline to declare and pay IRS/IRC withholding tax (retenções na fonte) deducted in September — Código do IRS, art. 98.º(3); 20 October — deadline to submit the monthly VAT (IVA) periodic return for August transactions; 26 October — deadline to actually pay that August VAT bill; missed deadlines risk fines ("coimas") plus late-payment interest, per the Autoridade Tributária's official calendar.
Two dates, one tight week
If you invoice Portuguese clients as a freelancer, or run a small Lda with staff, two dates on October's calendar matter more than any others: the 20th and the 26th. Companies and other taxable persons must also track obligations related to IRS and IRC, namely the declaration and payment of amounts withheld, due by 20 October. Four days later, the second hit lands: 26 October is the deadline for paying VAT under the monthly regime.
Both obligations sit with the Autoridade Tributária, run through the Portal das Finanças, and apply whether you're a one-person consultancy on recibos verdes or a registered company with employees. October marks another important stage in the fiscal calendar for individuals, self-employed workers and companies in Portugal, with contributors needing to watch several deadlines over the coming weeks.
What's actually due on the 20th
The withholding obligation covers tax deducted from payments made in September — this includes retentions applied to recibos verdes invoices from freelancers, salary withholdings, and rents. Under Portuguese tax law, amounts withheld must be delivered by the 20th of the month following that in which they were deducted. Separately, the same date closes the window for submitting the monthly VAT return itself: the periodic VAT declaration for the monthly regime relating to August is due by 20 October, covering operations carried out in August.
That's two filings converging on a single date — one for tax you withheld from someone else's income, one for VAT you charged on your own.
Then the VAT bill itself
Filing the VAT return isn't the same as paying it. The money itself follows six days later. By 26 October, taxable persons under the monthly VAT regime must pay the VAT calculated in the return relating to August. For freelancers who've crossed the €15,000 turnover threshold and lost their Article 53 exemption, this is the point where VAT charged to clients actually has to leave the bank account and reach the Treasury.
There's a structural reason October feels tighter than most months. Earlier in the year, August filings get pushed later because of the summer administrative slowdown — meaning September's catch-up obligations stack directly onto October's normal ones. The checklist for the month includes submitting the Social Security declaration by the 10th, delivering IRS/IRC withholdings and contributions by the 20th, submitting the monthly VAT return by the 20th, and paying VAT by the 25th. Also worth flagging for anyone employing staff in Portugal: from 1 October, the regular IRS withholding tables for employees and pensioners take effect again, replacing the temporary summer tables used between August and September. If you run payroll, your September deductions may already reflect the old summer rates — check before filing.
GrowIN's read on the calendar: the gap between the 20th (filing + withholding payment) and the 26th (VAT payment) is only six calendar days — meaning a freelancer who misses the first deadline is almost certainly going to miss the second one too, since both draw from the same invoice income and the same bank balance. Miss both, and you're not looking at one penalty exposure but two separate ones running in parallel, each accruing its own late-payment interest from a different trigger date. That compounding — rather than the size of either individual fine — is what makes October's calendar riskier than a typical month.
Why this matters more for foreigners
Freelancers who moved to Portugal recently, registered início de atividade, and are still getting used to recibos verdes often assume quarterly deadlines when they're actually on the monthly regime, or vice versa. Missing a 2026 fiscal calendar deadline can result in lost tax benefits, later corrections, or fines. None of this is optional small print — it's standard enforcement, and the Autoridade Tributária doesn't send much warning before penalties accrue.
"October compresses a month's worth of catch-up filings into a single week, and that's exactly when foreign freelancers get caught out," says GrowIN Portugal Editorial.
What to watch next
November brings the third-quarter VAT deadline for anyone on the quarterly regime, plus Modelo 30 and IUC vehicle tax obligations later in October. Anyone unsure which regime they're on, or whether their 2026 withholding rate is correct, should check their situation directly on the Portal das Finanças or consult an accountant before the 20th arrives. For a fuller walkthrough of freelancer tax obligations in Portugal — recibos verdes, VAT thresholds, and social security exemptions — see our guide at tax & NIF, and get in touch via services if you need help getting your filings in order before the next deadline lands.