Effectively Connected Income (ECI)

Effectively connected income, or ECI, is income that comes from actively doing business in the United States. The IRS splits a foreign person's US income into two buckets: ECI, earned through a US trade or business, and FDAP, the passive bucket of dividends, royalties, and similar payments. ECI is taxed the way American business income is taxed, at graduated rates on net profit after deductions, and it comes with a duty to file a US income tax return such as Form 1040-NR.

Whether your LLC's income is ECI depends on where the work happens and what touches the US. A developer in Argentina who serves clients through a US LLC, doing all the work from Buenos Aires with no US office, staff, or dependent agents, often has no US trade or business, so the profit is generally not ECI. Add US-based employees, inventory in US warehouses, or an office in Miami, and the analysis changes quickly.

This distinction drives which forms carry real tax. A foreign-owned single-member LLC with no ECI typically owes no US income tax, yet still files Form 5472 with its pro forma Form 1120 by April 15, because that filing is about reporting transactions, not taxing profit. Skipping it risks the $25,000 penalty even when the tax bill is zero.

Partnerships raise the stakes. If a multi-member LLC has ECI, section 1446 requires it to withhold US tax on each foreign partner's share, at rates that can reach up to 37%, and to report the withholding on Forms 8804 and 8805 alongside the Form 1065 due March 15. On a $50,000 ECI share, withholding can approach $18,500 before the partner ever files a personal return. Getting a clear answer on ECI early is one of the most valuable pieces of advice a non-resident founder can buy.