Withholding is where tax obligations land on the payer instead of the payee, which is why the questions feel urgent: get it wrong and the withholding agent, not the foreign payee, is the one liable. Every withholding question reduces to the same three: who is the payee, which regime applies to this payment, and which certificate stops or reduces the withholding. The regimes differ; the structure of the analysis doesn't.
FDAP withholding: §§1441–1442
Payments of U.S.-source fixed or determinable annual or periodical income (interest, dividends, royalties, certain service payments) to foreign persons carry withholding at a statutory 30% rate under §§1441–1442, unless a treaty reduces it or an exception (like the portfolio interest rules) applies. The rate the payer actually applies depends entirely on the documentation in hand before payment: no valid certificate, no reduced rate.
Partnerships with foreign partners: §1446
A partnership with income effectively connected to a U.S. trade or business must withhold on the effectively connected income allocable to its foreign partners under §1446, computed at the highest applicable rates, paid in installments, and reported per partner. Since the 2017 tax act, §1446(f) adds a second layer: on a foreign partner's transfer of an interest in such a partnership, the buyer generally must withhold 10% of the amount realized unless an exception is established. Partnerships discover these rules most often at the moment a foreign investor is admitted. The right time is before.
FIRPTA withholding: §1445
Dispositions of U.S. real property interests by foreign persons carry their own withholding under §1445, collected from the buyer at closing, with certificate procedures for reducing it when the actual tax will be less. It's the enforcement arm of FIRPTA, covered in more depth in our cross-border article.
W-8 or W-9: the determination that drives everything
The entire federal system runs on certificates. U.S. persons provide a W-9; foreign persons provide one of the W-8 family: W-8BEN for individuals, W-8BEN-E for entities, W-8ECI for income effectively connected with a U.S. business, W-8IMY for intermediaries and flow-throughs, W-8EXP for foreign governments and exempt organizations. Picking the right one is a classification question in disguise: what the payee is, and what the income is, decide the form. Our free Which W-8? tool walks the determination.
State withholding: nonresidents and composite returns
States run a parallel system aimed at a different gap: income flowing from a pass-through entity to owners who don't live there. Many states require the entity to withhold on nonresident owners' shares of state-source income, offer composite returns that let the entity file and pay on the owners' behalf, or both, with rates, thresholds, exemption certificates, and election mechanics that differ in every state. For a multistate partnership, the withholding matrix is a genuine per-state research project, which is exactly the comparison the State Tax Matrix builds, cited to each state's own authority.
Who, which regime, which form: answered from the law
Whether the question is a treaty rate on a royalty, §1446 installments for a new foreign partner, or one state's composite election, the AI Tax Assistant answers from the statutes, regulations, and state guidance with a clickable citation on every claim. Ask who withholds, how much, on which form, and check the authority yourself, one click away.
Shashank Sharma is the founder of Partnertax.ai, an AI tax assistant for tax professionals, built on cited IRS and Treasury sources.