2026 Tax Calendar: Key Dates Self-Employed Workers and SMEs Can’t Afford to Miss

Every fiscal year brings its own roadmap, and 2026 is no exception. Between the mandatory digitalization of invoicing, the now well-established system of self-employed contributions based on real income, and the usual round of deadlines —VAT, withholdings, installment payments, annual summaries and Corporate Tax— self-employed workers and SMEs face a year in which planning matters just as much as running the business itself. It’s not only about not missing a deadline, but about understanding what’s really changing and how it affects cash flow and day-to-day operations.

What’s new for the 2026 tax year

The big structural change remains the rollout of the Verifactu system, which requires invoicing software to meet strict technical requirements —traceability, tamper-proof records and the ability to report directly to the Spanish Tax Agency— under the timeline set by the Invoicing Regulation. Companies subject to Corporate Tax must already be operating with compliant software, while other taxpayers, including the vast majority of self-employed workers, have their own rollout date later in the year. In practice, this means checking as soon as possible whether your current invoicing software is certified, or whether your provider has an update scheduled, since continuing to issue invoices with non-compliant software can lead to inquiries and penalties.

Alongside Verifactu, the system of self-employed contributions based on real income brackets remains in place, with bases and contribution rates adjusted each year according to declared net earnings. Anyone who didn’t accurately estimate their income in previous years may face adjustments —in their favor or against them— that are best anticipated in cash flow planning rather than discovered when the notice from Social Security arrives.

Beyond that, the tax calendar keeps its usual shape: quarterly VAT returns (Form 303) and withholding returns (Forms 111 and 115) due within the first twenty days of April, July, October and January; annual informational summaries (390, 190, 180, 347) due at the end of January; the income tax campaign running from April to late June; and Corporate Tax filings in July for companies whose fiscal year matches the calendar year. The Tax Agency rarely goes easy on late-filing surcharges, so the real room for maneuver lies in getting organized in advance, not in scrambling on the last day.

What this means for your business

For a self-employed worker or an SME, these changes translate into very concrete decisions. First, check with your invoicing software provider —or with your advisor— whether your system already complies with Verifactu or has a migration date on the calendar; leaving it until the last quarter could mean running out of room to maneuver if technical issues arise. Second, anyone contributing based on real income should review their estimated net earnings mid-year and adjust their contribution if income is trending higher or lower than expected, to avoid surprises when the adjustment comes. Third, it’s worth blocking out the quarterly and annual filing dates on the business calendar with several days’ buffer before each deadline, using that time to gather invoices, reconcile bank accounts and review deductions before filing — not after.

It’s also a good time to double-check which expenses and incoming invoices are being correctly recorded as deductible —vehicle costs, utilities for business premises, per diems, professional association fees— since a miscalculated VAT or income tax figure in the first quarter tends to carry the error through the rest of the year. And for companies, planning ahead for the Corporate Tax installment payment helps avoid cash flow strain right before the July deadline.

At Zythos Business, we support self-employed workers and SMEs precisely in this groundwork: adapting invoicing to the new technical requirements, aligning contributions with the real state of the business, and managing the tax calendar with enough lead time so that every filing goes in with the numbers already reviewed — not under last-minute pressure.