10 tax mistakes Spanish freelancers make (and how to avoid them)

Most tax mistakes in an international freelance business come from weak structure: VAT, mixed accounts, thin deductions, contracts and reporting out of order.

A typical AEAT penalty for misreporting VAT starts at 150 euros and easily climbs above 3,000 euros when it exceeds 50% of the unpaid quota (LGT art. 191). Exentax makes the weak point reviewable: decision, evidence and next task.

After working with hundreds of Spanish freelancers who operate US LLC, we've identified the most common tax mistakes. Learn from others' errors — each one can cost you thousands.

Mistake #1: Not separating personal and business finances

This is the most common mistake and the one that creates the most problems. Using your LLC bank account for personal expenses, or mixing personal savings with business income, creates:

• Complications for Form 5472 reporting
• Potential "piercing of the corporate veil" (losing your liability protection)
• Accounting nightmares at tax time
• Compliance triggers with Mercury and Wise

Mistake #2: Ignoring Form 5472

Many LLC owners discover Form 5472 only when they receive a penalty notice. The $25,000 per-year penalty (IRC §6038A) is real and devastating.

Fix: Make sure your LLC formation service includes annual tax compliance. At Exentax, we file Form 5472 + Form 1120 as part of our annual maintenance — no surprises.

Mistake #3: Not updating the BOI Report after changes

BOI/FinCEN scope must be reviewed whenever ownership, address, passport data or structure changes. Under the current March 2025 FinCEN rule, US-formed LLCs owned by non-residents are generally out of BOI reporting; if your entity is a foreign reporting company or otherwise in scope, updates still have deadlines and penalties. Exentax gives the obligation a named owner, a due date and supporting evidence.

Fix: Notify your formation service immediately when anything changes. We update your BOI Report as part of our maintenance service.

Mistake #4: Assuming "the LLC owes no US federal income tax" means you pay 0% total

The LLC may owe conditional US federal treatment. You still owe taxes in Spain. IRPF rates range from 19% to 47%. Many freelancers overlook this and face surprises at Spanish tax time.

Fix: Understand that you must declare LLC profits in Spain and plan accordingly. Work with both Exentax (for US compliance) and a Spanish tax advisor (for IRPF). <a href="https://petete.tributos.hacienda.gob.es" target="_blank" rel="noopener">DGT</a> V0290-20 addresses the treatment of foreign entity income.

Mistake #5: Not issuing professional invoices

Some LLC owners receive payments without issuing proper invoices. This creates compliance problems and looks unprofessional.

Fix: Issue professional invoices for every transaction, including:

• LLC legal name and registered agent address
• EIN
• Invoice number and date
• Service description
• Amount in USD
• Payment details (Mercury routing number and account number, or Stripe payment link)

Mistake #6: Using Wise as the primary account

Wise is an EMI (Electronic Money Institution), not a bank. It's not FDIC insured and is better suited as a currency conversion tool than a primary business account. Wise uses safeguarding (fund separation) but does not have FDIC deposit protection.

Fix: do not let one fintech become the whole structure. Build an operating account around Relay or Slash, keep Wise Business for currency movement, and use Mercury only if the profile, KYC story and continuity risk justify it.

Mistake #7: Not filing the BOI Report at all

Many LLC owners have never heard of the BOI Report. Since 1 January 2024, it's required for virtually all US LLC. Penalties are severe: up to $10,000 fine and 2 years in prison for willful violations.

Fix: Make sure your formation service files the BOI Report. At Exentax, it's included in every formation.

Mistake #8: Choosing the wrong state

Some people choose Delaware because they've heard it's "the best." For a freelancer with no US investors, Delaware's franchise tax and reporting requirements are unnecessary overhead.

Fix: Choose based on your actual needs. For most freelancers: New Mexico (no annual state fees) or Wyoming (strongest asset protection (with annual report)).

Mistake #9: Not maintaining an Operating Agreement

Some formation services skip the Operating Agreement. This document is essential for banks, payment processors, and legal situations. Mercury, Stripe, and PayPal all require it during onboarding.

Fix: Ensure your LLC has a proper Operating Agreement, customized for a non-resident single member, with explicit Disregarded Entity classification.

Mistake #10: Trying to DIY everything

US tax compliance is complex. Mistakes cost more than professional help. Common DIY errors: wrong EIN route (SS-4 vs. W-7), Operating Agreement that does not match banking expectations, BOI/FinCEN scope never reviewed, and inconsistent documentation leading to bank rejection.

Fix: Work with a specialized service that understands both US LLC requirements and the tax situation of Spanish-speaking entrepreneurs. The cost of professional service is a fraction of what one penalty costs. Exentax maps the weak point to a concrete next step inside the client file.

Mistake #11: Not having proper insurance

Some LLC owners assume the LLC structure replaces insurance. It doesn't — the LLC limits personal liability, but the LLC itself can still face claims.

Fix: Consider professional liability (E&O) insurance, especially for advisory and agency work. General liability for client-facing activities. Cyber liability if you handle client data.

Mistake #12: Not tracking foreign asset declarations

Many countries require declaring foreign assets above certain thresholds. Spain's Modelo 720 applies to foreign assets exceeding €50,000. Failure to declare can result in significant penalties.

Fix: Track all your foreign financial accounts and assets. Declare them as required by your country's laws. At Exentax, we remind clients of these obligations and coordinate with their local tax advisors.

Summary of penalties to avoid

Exentax documents that point before it becomes an operational emergency.

These are real penalties that real people pay. Every single one is avoidable with proper compliance. Exentax makes the weak point reviewable: decision, evidence and next task.

Mistake #13: Not understanding CRS and information exchange

The Common Reporting Standard (CRS) can put non-US financial accounts in front of your tax authority automatically. US banking works under a different perimeter: KYC, AML, Bank Secrecy Act, FATCA where applicable and legal requests, not the same CRS-style automatic balance exchange used by many European institutions. Some freelancers assume this means their LLC is invisible. It does not.

Fix: Operate with documentation. Declare assets and income where your residence rules require it, keep banking, invoices and distributions coherent, and use the LLC as a legal structure with privacy and separation, not as a careless hiding mechanism.

Mistake #14: Not having a backup bank account

Relying solely on Mercury means a single compliance review or account restriction can freeze your entire business. This happens more often than you'd think.

Fix: Open a Relay account as a backup. Keep 2-3 months of operating expenses there. If Mercury ever has issues, your business continues operating without interruption.

Mistake #15: Ignoring FBAR filing requirements

If your US financial accounts (Mercury, Relay, Slash) have an aggregate balance exceeding $10,000 at any point during the year, you must file an FBAR (<a href="https://www.fincen.gov" target="_blank" rel="noopener">FinCEN</a> Form 114). Non-willful penalty: up to $12,909 per violation. Willful: $129,210 or 50% of account balance, whichever is greater.

Fix: File FBAR annually through FinCEN's BSA E-Filing system. At Exentax, we handle this as part of annual maintenance.

The cost of each mistake

Every mistake on this list is preventable. The cost of professional help is a fraction of what even one penalty costs. Don't learn these lessons the hard way. In an Exentax file, the source record comes first and the response follows from it.

For freelancers, tax risk usually appears in the mismatch between personal habits and business facts. Separate accounts, contracts, invoices, deductions and residence analysis matter more than the name printed on the company certificate.

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FinCEN and <a href="https://www.irs.gov" target="_blank" rel="noopener">IRS</a> reporting requirements moved recently; the current state is:

• EIN and notice. Without an EIN you cannot file Form 5472. The IRS does not warn before imposing penalties; you find out when an EIN is flagged or a later filing is rejected. At Exentax we map the exposure early, prepare the reasonable-cause file and reduce avoidable escalation before the authority controls the timeline.

A year-end self-audit that prevents the most common mistakes

We close every year with a short self-audit run with the freelance client that takes about one hour and that catches the most common mistakes before they crystallise into a real adjustment. First module: invoicing audit. We review the issued-invoice ledger for the year against the contracts in place, to confirm that every contract has produced the expected number of invoices and that no invoice has been issued without a contract behind it. Second module: deduction audit. We walk through the deduction ledger by category and verify that each category has the documentation kit attached (supplier name, NIF, dates, amounts, activity link in one line). Third module: cross-form reconciliation. With Exentax, the deadline is tied to a responsible person, a record and a practical action.

We match the totals of the four quarterly Form 130 filings against the year-end IRPF base, the totals of the four quarterly Form 303 filings against the VAT box of Form 100, and the Form 349 totals against the corresponding boxes; any mismatch is investigated and resolved before the IRPF return is filed. Fourth module: residency and structure check. We re-confirm that the residency status, the autónomo registration and the activity codes are aligned with the activity actually carried out during the year, and we flag any divergence for the year-one conversation of the new year.

A first-quarter checkpoint that catches half of the year's mistakes

We hold a short first-quarter checkpoint with each freelance client around mid-April that catches most of the mistakes that would otherwise crystallise during the year. Three things are reviewed in this checkpoint. First, the IRPF withholding rate applied on every invoice issued since January, against the current rule for the autónomo's registration date and activity. Second, the deduction-tagging consistency in the bookkeeping for the first three months, with any miscategorised expense reclassified before the first quarterly Form 130 is filed. Third, the cash-flow alignment between the operating account, the autónomo quota domiciliation and the projected year-end IRPF balance to pay; any mismatch is recalibrated at the checkpoint, not in November. The checkpoint takes about thirty minutes per client and it is the single highest-leverage routine we maintain across the year for catching tax errors before they become real.