Sofia had created a ceramics workshop. Just one. She did not know if it would work out, and did not want to formally open a business activity without being sure. “What if nobody comes? I will have a CAE open for nothing.”
What Sofia did not know is that there is an alternative: the ato isolado (isolated act). The legal way to invoice for occasional work without opening a formal activity.
What an ato isolado is
An ato isolado is a one-off economic transaction, without a habitual or regular character. You can provide a service, sell a product, or give a training session — once, occasionally — without needing to register as an independent worker with the tax authority.
The key word is isolated: something that happens once, not a regular pattern. Think of selling your used car — you would not open a car dealership because of it.
Situations where it makes sense:
- Giving a one-off workshop
- Doing occasional consultancy
- Selling a course or e-book you created once
- A single project before deciding whether to work independently long-term
How it works in practice
With an ato isolado there are no quarterly declarations and no Social Security contributions. The income is declared directly in your annual IRS return (Modelo 3, Anexo B, under the isolated acts category).
The coefficient applied is the same as in the simplified regime:
- 0.75 for services — you pay IRS on 75% of the amount
- 0.15 for product sales — you pay IRS on only 15% of the amount
Example — João, photography workshop:
- Charged €300 to 10 people = €3,000
- Services coefficient: €3,000 × 75% = €2,250 taxable
- Declared in the annual IRS under “isolated acts”
- Zero Social Security, zero quarterly declarations
What is the frequency limit
Portuguese law does not define an exact number of isolated acts per year. The criterion is habitualidade (habituality) — if the activity becomes regular, it is no longer isolated.
In practice:
- Once a year — no issues
- 2–3 times — grey area, depends on context
- More than 3 times — the tax authority may treat this as regular activity and require you to open a formal activity
Ato isolado vs. opening activity
| Ato isolado | Open activity | |
|---|---|---|
| Initial bureaucracy | None | Activity registration |
| Social Security | No | Yes (from 2nd year) |
| Quarterly declarations | No | Yes (VAT and SS) |
| Frequency | Occasional only | Unlimited |
| Withholding at source | Mandatory for companies | Can request exemption |
| Expense deductions | No | Automatic coefficient |
Choose ato isolado if:
- It is genuinely one-off
- You want to test an idea before committing
- The volume does not justify the full fiscal setup
Open activity if:
- You know you will invoice regularly
- Clients ask for invoices frequently
- You want to build an income history (useful for mortgage applications)
- You want to accumulate time towards a pension
A real decision story
Inês had created a template pack for social media and wanted to test the market:
- Month 1: Sold it as an ato isolado — 15 sales, €450
- Month 2: Saw there was consistent demand
- Month 3: Opened her activity on the Finance Portal
- Month 4: Invoicing regularly, with everything organised
The ato isolado was the test before the commitment. It worked exactly as it should.
The withholding point
If your client is a company, they are required to apply withholding tax on payment — even on an ato isolado. You receive less upfront, but that withheld amount is credited against the IRS you owe when you file your annual declaration.
With an open activity under the simplified regime, you can apply for an exemption from withholding. That option is not available for isolated acts.
✅ In summary
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The ato isolado lets you invoice legally without opening activity — for genuinely one-off situations. Income is declared in the annual IRS return; no Social Security, no quarterly declarations.
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The practical limit is 2–3 times per year — Portuguese law uses the concept of “habituality” rather than a fixed number. Above 3 isolated acts in the same year, the tax authority may challenge it.
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If the idea works, the next step is to open activity — with FIZ the setup is guided and invoicing is ready in minutes.
