Self-Employed Tax Return: What to Review Now That Filing Season Is Over

The tax return campaign for the 2025 tax year is behind us, but for a self-employed person, personal income tax (IRPF) doesn’t end when Form 100 is filed. With autumn 2026 under way, it’s a good time to calmly review what your last return revealed and to prepare for the year-end close, because the decisions you make now will shape the outcome of next year’s campaign.

Why a self-employed person’s tax return is different

An employee’s draft return usually shows little more than a withholding certificate. A self-employed person, on the other hand, declares net income from economic activity, calculated by subtracting deductible expenses from revenue, and that calculation depends on the accounts or record books being properly kept throughout the year. Under the direct estimation method, expenses necessary for the activity and properly backed by an invoice reduce your net income; under the objective estimation method (flat-rate “módulos”), the system is different and has its own rules, which are worth reviewing every year.

On top of this comes a key element: instalment payments. Throughout the year, the self-employed person advances part of their income to the tax authorities through Form 130 (or Form 131 under the flat-rate scheme). These payments are then deducted in the annual return. If the quarters were calculated in a rush or with incomplete data, the result of your return can come as a surprise: a larger amount to pay than expected or, conversely, an excess of advance payments that you have to claim back.

Where the tax authorities focus their scrutiny

The Tax Agency cross-checks more and more information: turnover declared for VAT, transactions reported by third parties, data from banks and payment platforms, and the amounts reported to Social Security. Discrepancies between what you file on Form 303, Form 130 and your tax return are one of the most common triggers for an official request. Likewise, mixed-use expenses, such as a vehicle or the home you work from, remain a closely watched area: the deduction requires genuine, exclusive use for the business or strict compliance with the proportions set by the regulations.

Your relationship with social security contributions also deserves attention. Since the reform introducing contributions based on actual income, the self-employed contribution depends on projected net income and is later adjusted using tax data. This means that what you declare to the tax authorities directly affects what you pay, or get back, in Social Security. It is therefore important that both figures are consistent and that the bracket you choose reflects the reality of your business.

As for penalties, the general regime penalises late filing and inaccuracies, with surcharges that grow the later you regularise. Correcting on your own initiative before a formal request arrives is, as a rule, considerably cheaper than waiting for the authorities to ask.

What this means for your business

First, review now, not next May, how your 2025 return turned out. Compare the income you declared with how 2026 is actually going: if your revenue has changed significantly, adjust your projected income with Social Security and the pace of your instalment payments.

Second, get your expense documentation in order before the year ends. An invoice with incomplete details or without proof of payment is an expense at risk. Ask for invoices with the correct tax details and separate personal from business expenses with sound judgement.

Third, plan your year-end. Before December, consider investments, contributions to pension schemes, or the timing of issuing certain invoices, always within what the rules allow and with a clear rationale, not on impulse. And if you work through a company, review the remuneration you pay yourself: paying personal income tax as a self-employed person is not the same as doing so through a company, and changing legal form calls for numbers, not hunches.

Finally, don’t leave your quarterly filings on autopilot. A Form 130 or a Form 303 that reconciles properly with your accounts is the best defence against any later audit.

At Zythos Business we support self-employed professionals and small businesses throughout the year, not just during filing season: we keep your accounts up to date, reconcile your quarterly filings with the books, and help you anticipate how much you’ll owe before the surprise arrives. If you’d like to review your tax situation before the 2026 year-end, we’d be happy to give you a hand.