Three Ways the 15% Rule Catches Freelancers Off Guard (Simplified Regime Portugal)

Most freelancers assume their Social Security contributions cover the 15% documented expense requirement in full. They don't. Only 10% of your gross services income counts, no matter how much SS you actually pay. What the AT form does not tell you is that this cap, not the specific deduction, not your quarterly adjustment, is what opens the gap.

That's the first way the rule catches people. There are two others: a first-year exemption trap, and a plateau at high income. Together, they cover most of the cases where freelancers end up with a surprise tax bill at IRS filing time.

For background on how the rule works and what counts toward it, see the 15% expense rule explainer. This post is about the ways it catches people who thought they were fine.

The 10% Social Security cap

Under the simplified regime, Seguranca Social contributions serve a dual purpose. You obviously need them for social protection. They also count toward the Art. 31 CIRS 15% documented expense requirement, but only up to 10% of your gross services income (Art. 31 nº13 a) CIRS). Your actual SS bill, at the standard 21.4% rate on 70% of income, works out to roughly 14.98% of gross, comfortably above that 10% ceiling. So the amount that counts is always the capped figure, never your full contribution.

This is easy to miss because the specific deduction (deducao especifica) of about €4,587.09 (2026) and the capped SS leg don't add together. AT takes whichever of the two is larger. Below roughly €30,580 gross, the specific deduction alone wins and covers the 15% threshold on its own. Above that, the capped SS leg takes over, and because it's capped at 10% while the threshold is 15%, a five-point-of-gross gap opens and never closes by itself.

Worked example: €80,000 gross, full-year Social Security, no adjustment

• 15% threshold: €12,000
• Actual SS paid: ~€11,984 (21.4% x 70% x €80,000)
• Capped SS leg (10% of gross): €8,000
• Specific deduction: ~€4,587.09 (2026)
• What counts: €8,000 (the capped SS leg, since it beats the specific deduction here)
• Shortfall to document: ~€4,000

Notice the actual SS bill (€11,984) is irrelevant to this calculation. Whether you pay the full amount or reduce it through the quarterly Declaracao Trimestral adjustment (which allows up to a 25% reduction, bringing it to roughly €8,988) makes no difference here: both figures are above the €8,000 cap, so both get capped to the same number. The quarterly adjustment mostly changes your cash SS bill, not your 15% coverage, because the cap usually binds either way.

The exact number depends on your income and your Social Security history for the year. The expense proof checker does this calculation for your specific situation. The point is not to memorize the breakeven: it is to check before year-end, not in June when you're filing.

The first-year trap

New freelancers are exempt from Social Security for their first 12 months of activity. The exemption starts from the date you registered, not from January 1.

During that window, the only automatic coverage you have toward the 15% threshold is the ~€4,587.09 (2026) specific deduction, since there's no SS to count at all (capped or otherwise). Below roughly €30,580 gross, that is enough. Above it, you have a shortfall.

The expat version of this trap is common enough to be worth naming. You moved to Portugal, registered a freelance activity, started picking up consulting work, and had a better first year than expected. The SS exemption felt like a gift. Nobody mentioned that the 15% documentation requirement was still running.

At €40,000 gross in year one, you need €6,000 documented. You have ~€4,587 automatic. The gap is roughly €1,413.

At €60,000 gross, the gap is roughly €4,413. That entire amount gets added to your taxable income before the 0.75 coefficient runs.

The shortfall is taxed at your marginal IRS rate. Depending on your total income, that could be 28.5%, 35%, or higher.

The high-earner plateau

This one layers on top of the 10% cap and matters once your business is growing toward six figures.

Actual SS contributions are not open-ended. The monthly contribution base is capped at 12 times the IAS (the social support index, roughly €537/month in 2026). In practice, this means your real annual SS bill plateaus at around €16,550 per year regardless of how high your gross income climbs.

That plateau only starts to matter for the 15% rule once it drops below the 10%-of-gross figure, which happens above roughly €165,500 gross. Below that, the 10%-of-gross cap is still the smaller, binding number. Above it, the plateaued ~€16,550 becomes the ceiling instead.

At €150,000 gross, you need €22,500 documented. The 10%-of-gross cap (€15,000) is still less than the ~€16,550 plateau, so €15,000 is what counts. Shortfall: ~€7,500.

At €200,000 gross, you need €30,000 documented. Now the plateau (~€16,550) is the smaller number, so that's what counts. Shortfall: ~€13,450.

The higher your income climbs past the plateau, the larger the documentation gap grows, at 15 cents per additional euro of income (the full 15% threshold, with no further automatic offset).

Most people reaching €150,000+ in freelance income in Portugal have a contabilista certificado (CC) who catches this. But not always, particularly in the first year someone crosses the threshold.

What to do about any of these

The answer in all three cases is the same, and it is simpler than it sounds.

Look at what you have already spent. Foreign supplier invoices you paid but never brought into e-Fatura. Software tools purchased with a personal card rather than your business NIF. Training courses. Equipment. Professional services from abroad.

These count toward the 15%. They are just not in the system yet. Registering a foreign invoice in e-Fatura or declaring it in Anexo B, Quadro 17-C takes a few minutes per invoice. The money left your account anyway.

If after accounting for everything you actually spent there is still a gap, then you can consider making qualifying business purchases before December 31. Not before.

The fact page at /facts/15-percent-expense-rule has the full reference on what qualifies and how the calculation works. The expense proof checker gives you the number for your specific situation.

Check in November. That leaves time to act if you need to. June is when it's already too late.

If you sell goods rather than services, a different problem applies: the simplified regime's 0.15 coefficient assumes an 85% cost ratio, and thin-margin sellers end up taxed on income they didn't earn. See goods sellers and the simplified regime coefficient.

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The figures above (the specific deduction, the 21.4% SS rate, the 12x IAS cap) reflect 2026. Tax rules change with the annual State Budget. Verify current figures with a certified accountant (contabilista certificado) or on the AT portal before filing.