Anexo SS: the IRS annex freelancers forget

Helena filed her IRS, breathed a sigh of relief and closed her laptop. Except one annex was left unfilled - one almost nobody knows about, and that many people skip without realising what they’re leaving out: the Anexo SS.

It’s not just any annex. It’s the bridge between your IRS and Social Security - and it’s the source of a bill that can land on your biggest client, without them even knowing.

What the Anexo SS is

The Anexo SS is the part of the IRS return (the Modelo 3) where a self-employed worker reports to Social Security their income from the activity and, above all, who their clients were during the year.

Filling it in is mandatory for most self-employed workers who had category B income - even those who were exempt from contributing (for example, in their first year of activity or because they combine it with employment). The obligation to file it doesn’t disappear just because you paid no contributions. (There are exceptions: those in a separate scheme, such as lawyers and solicitors under the CPAS, are not covered.)

Here you declare, entity by entity, how much you invoiced each client. And it’s on those figures that Social Security runs the numbers.

The number that decides everything: 50%

From what you declare in the Anexo SS, Social Security measures your economic dependence - how much you rely on a single client. The key threshold is 50%: if more than half of what you invoiced in the year comes from a single entity, two things may follow - provided the other conditions are met (which we’ll see next):

Contrary to what many people think, the client does not wait until 80% to start paying: the obligation arises just above 50% (provided you are subject to the contribution obligation and invoiced, in services, at least 6 times the IAS value in the year). The 80% only decides how much they pay.

The bill that lands on your client: the contracting entity

When a client passes 50% of what you invoiced in the year (and you are subject to the contribution obligation, with annual service income of at least 6 × the IAS), Social Security can classify it as a contracting entity (entidade contratante) and require it to pay a contribution on the services you provided. How much it pays depends on your degree of dependence:

The worker pays not a cent more for this: the contribution is the client’s alone.

Example: Helena and the agency

Helena is an illustrator. In 2025 she invoiced €40,000 in total, of which €36,000 to a single agency. Here’s the calculation Social Security makes:

Since the dependence (90%) passes 80%, the agency pays at the higher rate, 10%. In the second half of 2026 it receives a notice from Social Security to pay €3,600. Helena pays not a cent more.

Example: Diogo and the lower rate

Diogo is a developer. He invoiced €30,000, of which €19,500 to one client - 65%. He’s in the 50%-to-80% band.

The result: Diogo becomes economically dependent (one of the requirements for the cessation benefit) and the client is a contracting entity - it’s just that, because the dependence is between 50% and 80%, it pays at the lower rate, 7%: 7% × €19,500 = €1,365. The rule is the same as Helena’s; only the rate changes, because the degree of dependence changes.

How it works in practice

You don’t have to do the maths or warn anyone: the process is automatic.

1. You file your IRS with the Anexo SS by 30 June, declaring how much you invoiced each entity.
2. The tax authority passes that data to Social Security.
3. In the second half of the year, Social Security cross-checks the figures, identifies the entities above 50% (under the conditions above) and notifies them to pay. You do nothing - you just have to have filled the annex in correctly.

Warning: the most common mistake is rushing the IRS and skipping the Anexo SS, or entering the per-entity figures wrong. Without it, Social Security can’t work out your economic dependence - and you may lose the access to the cessation benefit you’d be entitled to, or create mismatches that cause headaches later. Always check that the amounts per client match what you actually invoiced.

✅ In summary

1. The Anexo SS links your IRS to Social Security and declares, entity by entity, how much you invoiced. It’s mandatory for most self-employed workers with category B income (there are exceptions, such as the CPAS), even those exempt from contributing.

2. The threshold is 50%: if more than half your income comes from a single client, you become economically dependent - one of the requirements for the cessation benefit - and that client can become a contracting entity, obliged to pay Social Security 7% (dependence over 50% up to 80%) or 10% (over 80%) - at no cost to you.

3. With FIZ your income per client is organised throughout the year, so the Anexo SS stops being a puzzle at the deadline - filling it in becomes a matter of confirming figures that already exist. See the plans.