Self-Employed and Small Businesses: What Fall 2026 Brings on the Tax Front

Summer is over on the tax front, and September brings renewed activity at the Spanish Tax Agency and Social Security. For self-employed workers and small businesses, these weeks tend to bring two issues into focus: the adjustment of RETA contributions based on actual income, and the start of the year’s final round of quarterly tax obligations. Neither is new, but each year comes with its own wrinkles that can turn into an unexpected charge -or a refund- if you don’t plan ahead.

Contribution adjustments: a growing presence

Since the income-based contribution system replaced the old fixed brackets, every self-employed worker pays provisional contributions throughout the year based on their declared income forecast, and Social Security then adjusts that figure once actual net income is known from the personal income tax return. That adjustment isn’t immediate: it lags behind the tax year it relates to, and notifications or charges often arrive months after the return has been filed. Those who earned more than expected may face an additional payment; those who earned less are entitled to a refund. The real issue isn’t usually the amount but the surprise: many self-employed workers don’t track what they’re invoicing against the contribution base they’re actually paying into, so the adjustment lands without ever having been budgeted for.

On top of that, the income forecast for the current year can -and should- be corrected if actual activity has clearly diverged from what was estimated at the start of the year; doing so in time keeps the gap between provisional contributions and actual income from widening even further ahead of the next adjustment.

The final stretch of the year: quarterly returns, adjustments and e-invoicing

At the same time, the third quarter is drawing to a close, bringing the VAT return (Form 303) and, for those under direct estimation, the income tax installment payment (Form 130) or professional withholdings (Form 111). These aren’t filings that leave room for last-minute surprises: it’s worth checking in advance that the quarter’s deductible expenses are properly documented and recorded, and that no corrective invoice or rebate is still pending before closing.

Add to this a horizon that’s no longer distant: the rollout of mandatory e-invoicing between businesses and self-employed workers keeps moving forward, and invoicing systems will need to meet the traceability and immutability requirements set out in the regulation known as Veri*Factu. Although the deadlines vary depending on the type of taxpayer, adapting your invoicing software with time to spare avoids the last-minute rush -and mistakes.

What this means for your business

In practice, this translates into some very concrete decisions. First, check as soon as possible whether your current contribution base reasonably reflects what you’ll declare this year; if there’s a significant gap, request the bracket change yourself rather than waiting for the automatic adjustment. Second, if you know an additional contribution charge is coming for a year that’s already closed, set the corresponding cash aside rather than assuming it’s already spent. Third, before filing this quarter’s Form 303 and 130, take the time to reconcile income and expenses against what your invoices actually support: this is the cheapest moment to catch a wrongly deducted VAT charge or an unsubstantiated expense, long before a tax office request does it for you. And fourth, if your invoicing software still doesn’t meet the requirements that e-invoicing will demand, start looking into migration now: switching systems under pressure, right before the deadline, always costs more and brings more mistakes.

At Zythos Business we keep a close eye on each of these fronts -contributions, quarterly filings, regulatory changes- so our self-employed and small-business clients don’t have to track every bulletin themselves. We review contribution bases ahead of time, prepare tax forms with enough margin to catch issues before filing, and guide the transition toward the new invoicing requirements, so that every tax change becomes routine business as usual rather than a last-minute scramble.