Form a US LLC from Spain

Non-resident founders without a US SSN or ITIN file Form SS-4 by fax, listing 'Foreign' as the responsible party's ID type. Expect 4-7 business days for processing once the IRS confirms receipt of the fax. Spanish founders sometimes enter their NIE (Número de Identidad de Extranjero) or DNI number into a field formatted for a US SSN -- don't; the correct entry for a foreign responsible party is 'Foreign,' with your NIE/DNI serving only as supporting identification if requested separately.

Mercury and Relay both accept Spanish applicants once the LLC and EIN exist, with no US visit needed. Spain has no exchange controls and the euro is freely convertible, so there's no regulatory friction moving money between Spain and your US LLC -- the practical consideration is simply cost-efficiency, where most founders use Wise for day-to-day EUR/USD conversion on operating expenses rather than routing everything through a traditional Spanish bank's international wire fees.

Wyoming suits most Spanish founders in the SaaS, consulting, or digital-product space who aren't planning to raise institutional funding -- $60/year, no franchise tax, no public disclosure of ownership. Delaware becomes the better choice specifically if you're building a startup aimed at Spanish or pan-European VC funds, several of which (particularly Barcelona and Madrid-based funds active in the US-facing SaaS space) now default to expecting Delaware structures for portfolio companies with US market ambitions.

Wyoming's annual report and $60 fee are due by the first day of your formation anniversary month. Delaware's franchise tax (up to $400 under 2026 rates) is due every June 1. Form 5472 and the pro-forma 1120 are due April 15, with an automatic extension to October 15 via Form 7004. Spain's own IRPF filing season runs April through June for the prior tax year -- worth aligning your US LLC's bookkeeping so the numbers you need for your Spanish declaration are ready well before that window opens.

Registering as autónomo is how most Spanish founders start, and for a solo consultant or small freelance operation it works fine -- until it doesn't. The ceiling usually shows up in one of two ways: Spanish social security contributions for autónomos scale with revenue in a way that starts to feel punitive once you're earning meaningfully more than a typical salary, or US clients and platforms start asking for a US entity before they'll sign a contract or set up recurring billing. Neither problem is solved by working harder as an autónomo -- they're structural. A US LLC doesn't replace your autónomo registration (you may still need it for Spanish-side invoicing and social security purposes depending on your residency status), but it gives you a separate, dollar-denominated entity that US clients, Stripe, and US-based SaaS billing tools treat as a normal counterparty rather than a foreign freelancer requiring extra paperwork.

The US-Spain income tax treaty has been in force since the 1990s, with a protocol effective 2019 that lowered withholding rates on dividends, interest, and royalties between the two countries -- among the more founder-friendly updates in recent transatlantic tax treaty history. For a disregarded single-member LLC with a non-resident owner, the baseline Form 5472 and pro-forma Form 1120 filing is required annually regardless of income or treaty status, with a $25,000 minimum penalty for missing it. If you remain a Spanish tax resident (which most autónomos are), any income you personally draw from the LLC needs declaring on your Spanish IRPF return -- the treaty helps avoid double taxation on that income, but doesn't eliminate the Spanish-side declaration requirement.