2026 Tax Calendar: What Self-Employed Workers and SMEs Need to Watch to Avoid Trouble with the Tax Office

Every tax year comes with its own list of dates, forms and obligations, and 2026 is no exception. For self-employed professionals and small businesses, the difference between staying on top of taxes and letting things pile up usually comes down to something decidedly unglamorous: a well-organized calendar and someone keeping an eye on it. The Tax Agency doesn’t forgive oversights, and penalties for filing late — even when the result is zero or a refund — remain one of the most common, and most avoidable, headaches out there.

The bulk of quarterly obligations (VAT via Form 303, personal income tax prepayments via Form 130 or 131, and withholdings via Form 111 or 115) keeps its usual rhythm: filing within the first twenty calendar days of the month following the close of each quarter, with the fourth quarter extended to the end of January of the following year. On top of that come the annual summaries filed in January (Form 390 for VAT, Form 190 for withholdings, Form 347 for transactions with third parties) and, for companies, Corporate Income Tax in July. None of this is new, but it bears repeating: a good share of the penalties we handle at firms like ours don’t stem from calculation errors, but from deadlines missed due to date confusion or over-reliance on manual reminders.

Verifactu and e-invoicing: the real shift in 2026

Beyond the usual calendar, 2026 is the year the requirement to use certified, traceable invoicing systems — known as Veri*Factu — starts effectively applying to self-employed workers and SMEs, following an earlier phase aimed mainly at software developers. In practice, this means the invoicing software you use must guarantee that every invoice is recorded completely and cannot be altered, with the ability to send those records to the Tax Agency. Anyone still invoicing through Excel templates or non-compliant software risks falling foul of the law the moment the requirement kicks in for them, with penalties to match. Layered on top of this is the parallel rollout of mandatory e-invoicing between businesses, whose scope will keep expanding over the coming years.

On the social security side, the system of self-employed contributions based on net income brackets remains in place and requires revisiting your income forecast every year: contributing below what you actually end up earning — or above it — exposes you to a later adjustment with Social Security that can mean an additional payment or a refund, depending on the case. Adjusting your bracket to match your business’s real numbers, rather than whatever figure was convenient when you first registered, heads off unpleasant surprises when the adjustment comes through.

What this means for your business

Translated into concrete action, here’s what a self-employed worker or SME should be checking right now. First, confirm that your invoicing software is adapted — or on track to be adapted — to the new traceability requirements, rather than waiting for a notice to arrive; switching systems with time to spare is far cheaper than doing it under pressure. Second, don’t leave quarterly filings until the last day of the deadline: closing the books a week ahead lets you catch missing invoices, misrecorded expenses or discrepancies with previous quarters before they turn into a problem with the Tax Agency. Third, review your self-employed contribution bracket against this year’s actual figures, not an old estimate, to avoid both an unexpected adjustment and months of overpaying for no reason. And fourth, if your business has grown, check whether you still qualify for the same tax regimes (modules, equivalence surcharge, VAT exemption) or whether it’s time to review your situation before the Tax Agency does it for you through a formal request.

None of these decisions requires deep technical expertise, but they do require sustained time and attention throughout the year — precisely what most self-employed workers and small business owners don’t have to spare between serving clients and running day-to-day operations. At Zythos Business, we turn that tax calendar into something that doesn’t depend on anyone’s memory: we review deadlines, bookkeeping and contributions continuously, not just as deadlines approach, so that every form is filed correctly and on time, and so that decisions like your contribution bracket or invoicing system are made with real data and room to react — not under the pressure of a penalty that’s already landed.