Self-Employed Contributions Based on Real Income: How the Brackets and TGSS Adjustment Work

Since 2023, self-employed workers in Spain have paid Social Security contributions based on their real income, rather than on a freely chosen base unrelated to actual earnings. The system works through brackets: the higher an individual’s net income, the higher the contribution base they’re assigned — and with it, the monthly payment. In 2026 this model remains fully in force, and it’s still the main source of surprises, both pleasant and unpleasant, once the dreaded adjustment notice arrives from the Tesorería General de la Seguridad Social (TGSS, Spain’s Social Security Treasury). Understanding how the bracket is calculated and what the later adjustment involves helps avoid nasty surprises and makes it easier to plan the business’s cash flow.

How Does the Bracket System Work?

The contribution isn’t based on revenue, but on net income: earnings minus deductible business expenses, plus an additional flat-rate deduction for hard-to-justify expenses (usually a fixed percentage of net income, slightly higher for company-linked self-employed workers). That monthly net income is then slotted into a table of fifteen brackets, each with a minimum and maximum contribution base. Within their bracket, the self-employed worker can choose any base between those limits, which determines that month’s contribution.

When registering, or at the start of each tax year, the self-employed worker must estimate their annual net income and choose the provisional base for the corresponding bracket. This is a forecast, not a fixed figure: the law allows the contribution base to be changed up to six times a year to reflect how the business is actually performing (better or worse than expected), moving to a different bracket if needed. This flexibility matters: the closer the forecast is to reality, the smaller the later adjustment will be.

Changing Your Base During the Year

Any bracket change takes effect from the two-month period following the request, not immediately, so it pays to plan ahead rather than react at the last minute. A common mistake is leaving the base on “autopilot” for the whole year, especially in seasonal businesses or those with irregular income: if a self-employed worker earns heavily in the final quarter but stays in a low bracket, the gap between what was paid in and what was actually earned builds up and shows up in full at adjustment time. Keeping the books up to date — or at least having a reliable quarterly estimate of net income — is really the only way to land in the right bracket without relying on guesswork or rough calculations.

The TGSS Adjustment: What It Is and When It Arrives

Once the annual income tax return has been filed, the Tax Agency passes each self-employed worker’s final net income figure on to the TGSS. Social Security then compares it against the bases actually used to contribute month by month that year and calculates the difference. If the worker paid in more than their real income warranted, the TGSS automatically refunds the excess. If they paid in less, it claims the difference through an adjustment payment, usually with a set deadline and no surcharge if paid within that window. This adjustment doesn’t happen in the same year as the activity itself, but later, once that year’s income tax season has closed — worth keeping in mind, since the monthly contributions paid shouldn’t be treated as final until that notice arrives.

A simple example illustrates the mechanism: a self-employed worker who forecast €20,000 in annual net income and contributed all year at the corresponding bracket, but who ultimately declares €30,000 in actual net income, will have to pay the difference between the initial bracket’s contribution and the one that matched those €30,000, multiplied by the months underpaid. The reverse case — forecasting too high and earning less — triggers a refund. The most common mistake isn’t deliberately under-contributing, but failing to review the forecast during the year and then finding the adjustment shows up as an unexpected debt months later.

At Zythos Business, we support self-employed workers and small businesses precisely on this blind spot: we regularly review the actual net income of the business, adjust the contribution base to the correct bracket before any gap can build up, and anticipate the likely outcome of the adjustment so it never comes as a surprise. Keeping the books current does more than keep the accounts tidy — it prevents overpaying Social Security or discovering a debt that could have been foreseen months in advance.