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The short answer: an SLU is an SL with one shareholder. The legal form, the tax treatment, the liability, and the compliance obligations are identical. The only thing that changes is the disclosure label, because Spanish company law requires a single-shareholder limited company to flag itself as "unipersonal" until it has two or more partners.
If you are deciding which to set up, the question is not really SL vs SLU. It is "how many partners will I have on day one?" One: SLU. Two or more: SL. Both convert into the other any time partners come or go.
This guide covers the legal mechanics, the day-one paperwork that differs, the misconception that costs founders money, when an SL or SLU is right at all (versus autónomo or SA), and how to switch between SL and SLU when the partner count changes.
The decision is administrative, not strategic. The strategic question is whether to incorporate at all, which is the SL versus autónomo question covered in self-employed or limited company.
Sociedad limitada is the standard limited company under the Ley de Sociedades de Capital. The company is a separate legal person from its owners. Profit is taxed at the company level under Corporate Tax. Owners (called socios or partícipes) hold participaciones (not shares; participaciones cannot be freely traded the way shares can).
Setup involves:
Once registered, an SL with two or more partners operates without any unipersonal disclosure. Voting rights track participaciones. Profit distributions follow the partnership agreement (estatutos sociales) and partner-by-partner declarations on Modelo 100.
A Sociedad Limitada Unipersonal is the same legal vehicle as an SL with one practical difference: a single shareholder owns 100% of the participaciones. Spanish law requires you to disclose this status:
The disclosure is the only meaningful operational difference. Capital, tax, liability, voting (you vote alone), and reporting are otherwise the same as an SL.
The most common scenario for an SLU is a solo founder incorporating to obtain limited liability and a more institutional face for clients. Solo professionals running an SL on their own without registering as unipersonal are technically non-compliant, with personal liability exposure for debts during the period they failed to declare.
This is the entire difference. Everything else is the same.
The disclosure rule exists to protect creditors. A single shareholder controls all decisions, so the law requires transparency about that control.
Both pay Corporate Tax under the same rules. There is no SLU tax surcharge, no separate brackets, no different deduction rules.
There is no difference between SL and SLU at any stage of this calculation.
Both shield personal assets from business debts. Both create personal exposure when the director acts unlawfully (wrongful trading, failure to file insolvency, fraud).
The one liability difference: an SL with a single shareholder that has not declared unipersonalidad makes the sole shareholder personally liable for company debts (Article 14 LSC). The fix is the registration. Once you declare the unipersonalidad and update the registry, the limited liability shield re-engages prospectively. Liabilities incurred during the non-disclosed period remain personally yours.
This is the single concrete reason to bother with the SLU declaration on time.
Setup is identical: name reservation, share capital, notary, NIF, Registro Mercantil, Modelo 036, social security alta. Allow two to four weeks and €1,000 to €1,500 once you include all fees.
The SLU adds:
Annual obligations are identical: legalise books by 30 April, file annual accounts by 31 July, file Modelo 200 by 25 July, pay quarterly retentions and VAT.
Ongoing gestor / accountant fees are unaffected by the unipersonal flag. Budget €700 to €1,800 a year either way.
The conversion path from autónomo to SLU is the most common way solo founders end up here. See self-employed or limited company for the break-even maths that decides whether the move is worth it.
If you start as an SL and one partner buys out the other, the company becomes unipersonal automatically and you have six months to declare the SLU status at the registry.
Conversion happens by default with partner-count changes. The required declaration timing:
In both directions, the company itself continues. Same NIF, same legal personality, same contracts, same bank accounts. There is no liquidation, no new escritura, no tax event from the change of unipersonal status alone.
For the typical solo or small-team founder, the SL or SLU is the answer. The autónomo route is faster and cheaper to start, but does not protect personal assets. SA is overkill until you cross into significant capital raising.
Is SLU a different legal form from SL? No. It is the same legal form (sociedad limitada) with a single-shareholder disclosure obligation.
Does SLU pay more tax than SL? No. Both pay Corporate Tax at 25%, with the same 15% reduced rate for new entities on the first two profitable years.
What is the minimum capital for an SLU? €1 since the 2022 Crea y Crece law. Until reserves reach €3,000, you must keep 20% of net profit as a legal reserve, and partners are personally liable for the gap if the company is wound up insolvent. Most founders still capitalise at €3,000.
Do I need a notary to convert SL to SLU or SLU to SL? No notary deed is needed for the change of unipersonal status itself. You record the change at the Mercantile Registry and update commercial documents. Adding a new partner generally requires a notarised participaciones transfer or capital increase.
Can an SLU have employees? Yes. The unipersonal flag relates to ownership, not staffing. An SLU can hire employees just like any SL.
What happens if I forget to register the unipersonal status? You bear personal liability for company debts incurred during the unregistered period (Article 14 LSC). Register as soon as the omission is identified. Future debts revert to limited liability once the registry is updated.
renn handles SL and SLU constitution end to end: name reservation, capital deposit, notary coordination, Registro Mercantil filings, Modelo 036, social security alta, and the unipersonal declaration where it applies. Real accountants on the file, the platform handling the rhythm. If you are still deciding between staying autónomo and incorporating, renn handles autónomo registration online as well, and migrates the activity into an SL or SLU when the numbers justify it.
