Tax Back-to-School: The Hacienda Calendar Self-Employed Workers and SMEs Can’t Ignore

Summer is coming to an end, and with it arrives one of the busiest stretches of the year for Hacienda’s demands on self-employed workers and SMEs. Between late September and the close of the year, businesses face a pile-up of quarterly returns, instalment payments, module reviews and, for many companies, the first mandatory steps toward electronic invoicing. The structure of this calendar isn’t new, but it’s worth reviewing carefully, because a slip-up on any of these dates translates directly into surcharges or a formal request from the Tax Agency.

An autumn with a packed tax agenda

Most of the post-summer obligations revolve around the third quarter of the tax year. Form 303 (VAT) and the personal income tax instalment payments (Form 130 for direct estimation, Form 131 for modules) are usually filed in the window that opens in early October and closes around the 20th, unless payment is set up by direct debit, which moves the deadline forward a few days. Depending on the business activity and legal structure, this is joined by withholdings on employees and professionals (Form 111) or on landlords (Form 115), and for companies with corporate tax instalment payments, Form 202.

This year, an added factor joins the usual calendar: the rollout of the new electronic invoicing and anti-fraud rules (Verifactu), whose phased implementation continues through 2026 and is progressively requiring companies and self-employed workers to adapt their invoicing software to the technical requirements set by Hacienda. Anyone still invoicing with loose templates or non-compliant software has a compelling reason, in this part of the year, to review their system before the obligation catches them without room to react.

It’s also worth remembering that Hacienda steps up its cross-checking of information during these months: it compares what’s declared for VAT and income tax against data it receives from third parties (banks, payment platforms, suppliers) and against Social Security contribution bases — especially relevant now that self-employed workers contribute based on actual net income. Any discrepancy between what’s declared and what Hacienda already knows through other channels usually results in a letter from the tax authorities, not always accompanied by a penalty, but always by extra work to justify the difference.

What this means for your business

In practical terms, this pile-up of deadlines calls for three concrete decisions. The first is about cash flow: it’s worth setting aside, in advance, the estimated amount for VAT and the income tax instalment payment (or corporate tax), so the spike in expenses doesn’t hit all at once in mid-October. The second is about reviewing your figures: this is the moment to check that third-quarter income and expenses are properly recorded, and, for those taxed under direct estimation, that the net income forecast is still realistic, to avoid over- or under-declaring the instalment payment. The third, and increasingly urgent, is technological: if the business hasn’t yet checked whether its invoicing software meets the requirements of the new anti-fraud rules, this is the quarter to do it, avoiding a last-minute scramble once the obligation takes effect for your business category.

For those who contribute as self-employed workers under the net income system, September and October are also a good time to check whether the contribution base chosen at the start of the year still matches actual projected income, since a significant mismatch can force a regularisation of contributions once Social Security cross-checks the data against the year’s income tax return.

Avoiding penalties is cheaper than fixing them later

The cost of a tax slip-up is almost always higher than the cost of avoiding it: a surcharge for filing late, even when the return itself is correct, already means paying a percentage that could have been saved with a simple calendar alert. That’s why, beyond just knowing the dates, what really matters is having a system — whether managed in-house or with professional support — that anticipates each obligation with enough lead time to gather documentation, review the figures and file without last-minute rushing.

At Zythos Business, we support self-employed workers and SMEs precisely in that anticipation: we keep the tax calendar up to date, check that each return matches the real accounting before filing, and give early warning of any regulatory change that could affect the business — so these appointments with Hacienda stop being a source of stress and become just another well-managed routine.