The withholding amount is the US-source portion of the payment multiplied by the applicable rate, and four questions in order produce both numbers: who is being paid, where the work was performed, what kind of payment it is, and what the treaty says. Work performed outside the United States is foreign-source and outside withholding entirely. The US-source portion is withheld at 30% unless a valid W-8 claims a treaty rate. The payment is reported on Form 1042-S for the calendar year either way, even when the amount withheld is zero.
- Who: a US person files a W-9 and sits outside this calculation. A foreign person files a W-8.
- Where: services are sourced where the work is performed, so only the US-source share enters the calculation. On a $10,000 payment with 25% of the working days in the United States, that share is $2,500 and the remaining $7,500 is outside withholding.
- What: the income type selects the treaty article and the 1042-S income code.
- Treaty: with a valid W-8BEN-E, no US permanent establishment and limitation-on-benefits qualification, the business-profits rate on that $2,500 can be 0%. With no valid form it is 30%, or $750.
- An individual claiming a treaty exemption on US services pay uses Form 8233 rather than W-8BEN, which requires a US TIN and a 10-day waiting period after the form is sent to the IRS. Until both are met the payment is withheld at 30%.
A US business paying a foreign contractor usually meets the withholding question the same way: an invoice arrives, someone remembers a rule about 30%, and nobody is sure whether it applies to this payment. The calculation itself is not long. It is a sequence of four questions, each of which changes the answer to the next, and the difficulty is that the inputs live in different places (e.g., the payee's W-8, the contract, the treaty text, and IRS Publication 515). This guide walks the sequence in the order a withholding determination actually runs, shows what a manual calculation requires at each step, and closes with what a tool does with the same inputs.
The default is set by statute: absent a valid treaty claim or an exception, a US payor withholds 30% of the US-source amount paid to a foreign person (Internal Revenue Code sections 1441 and 1442). Everything below is about whether that default applies to your payment, and at what rate.
Step 1: Who is being paid
The first input is the payee's status, and it is a legal test, not a geographic one. A US person (e.g., a citizen, a green-card holder, or a US entity) files a W-9 and sits outside this calculation entirely, because the 1099 rules apply instead. A foreign person files a W-8 (W-8BEN for an individual, W-8BEN-E for an entity), and that form is the payor's evidence for every later step, including any treaty claim.
Two details on the form matter for the arithmetic. First, the form must be valid on the payment date. A W-8BEN or W-8BEN-E generally remains valid through the end of the third calendar year after it is signed, provided that nothing on it has changed (Treasury Regulation section 1.1441-1(e)(4)(ii)). Second, a treaty claim is made on the form itself (Part II of the W-8BEN-E, or Part II of the W-8BEN, including the article and the rate claimed), and a claim for a reduced rate generally requires a taxpayer identification number. One carve-out matters for contractors: an individual claiming a treaty exemption on pay for personal services performed in the United States does not make that claim on W-8BEN at all. It runs through Form 8233, with its own US TIN requirement and 10-day waiting period. Accordingly, an expired W-8, or a W-8 with no treaty claim, should be treated as no treaty claim: the calculation proceeds at the 30% default.
Step 2: Where the work was performed
The second input decides how much of the payment is in scope at all. For services, US tax law sources the income to the place where the work is physically performed (Internal Revenue Code section 861(a)(3) for US-source and section 862(a)(3) for foreign-source). Where the contractor sits, where the payor sits, and which bank receives the money do not change that result.
Here, the practical test is a calendar. A foreign consultant who performs all of the work from abroad has earned foreign-source income, and a US payor does not withhold on it at all (the W-8 is still collected and kept on file). A consultant who spends part of the engagement on site in the United States has earned partly US-source income, and the US-source portion is normally allocated by working days (Treasury Regulation section 1.861-4(b)). For a $10,000 fee with 25% of the working days in the United States, the amount in scope is $2,500, not $10,000.
Royalties follow a different sourcing rule. A royalty is US-source when the property (e.g., a copyright, a patent, or a licensed format) is used in the United States (section 861(a)(4)), wherever the licensor lives and wherever the contract was signed. Director fees and prizes have their own rules, which is one reason the income type is the next question rather than the first.
Step 3: What kind of payment it is
The third input is the character of the payment, because each income type carries its own treaty article, its own 1042-S reporting code, and in some treaties its own rate. For a foreign contractor the common types are (1) compensation for services, (2) royalties for the use of intellectual property, and (3) director fees paid to a board member. A contract that mixes them (e.g., a developer paid partly for hours worked and partly for a license to the code) should be split, and each part calculated on its own.
The label on the invoice does not control. A payment described as a "consulting fee" that is in substance a license of software is a royalty for this purpose, and the treaty article that governs it is the royalty article, not the business-profits article. This is the step where most manual calculations go wrong, and it is the step the treaty text decides.
Step 4: What the treaty says
The fourth input is the treaty between the United States and the payee's country of residence, and it is read in a fixed order: the residence article (is this person a resident of the treaty country), the limitation-on-benefits article (is this person entitled to the treaty at all), and then the article for the income type, with its rate and its conditions.
For services performed by an independent contractor, most current US treaties route the income through the business-profits article. Under that article, the United States may tax the income only if the contractor has a permanent establishment in the United States (e.g., a fixed place of business, or a dependent agent concluding contracts), and a foreign company whose staff make a short on-site visit generally has none. With a valid W-8BEN-E claiming that article, the treaty rate on the US-source portion is 0%. That route belongs to entities. An individual contractor claiming the same exemption on pay for services performed in the United States does not claim it on W-8BEN; the claim runs through Form 8233, which requires a US TIN and a 10-day waiting period after the form is sent to the IRS before the exemption can be applied. Royalty articles work differently: many set a rate directly (0%, 5%, 10%, or 15% depending on the treaty and, in several treaties, on the kind of property), and some carve particular property (e.g., film and television rights, or industrial equipment) out of the reduced rate. Director-fee articles in most treaties allow the country of the paying company to tax the fee, so the treaty typically gives no reduction there at all.
Importantly, a treaty rate is not a fact about a country. It is a fact about one article, applied to one income type, subject to that article's conditions, for a payee who qualifies under the residence and limitation-on-benefits tests. The citation for the calculation is the article and paragraph, and a memo that cannot name them has not finished the calculation.
Putting the four inputs together
The withholding amount is the US-source portion of the payment multiplied by the applicable rate. Using the example above, a UK software consultancy (a UK Ltd) is paid $10,000 for work by its staff, with 25% of the working days in the United States, and provides a valid W-8BEN-E claiming the business-profits article of the US-UK income tax treaty: it has no US permanent establishment, and it qualifies under the treaty's limitation-on-benefits article.
- US-source amount: $10,000 × 25% = $2,500 (the remaining $7,500 is foreign-source and outside withholding).
- Treaty rate on the US-source amount, with a valid claim and no US permanent establishment: 0%. Withholding: $0.
- The same payment with no valid W-8BEN-E: 30% × $2,500 = $750 withheld.
Had the payee been an individual UK consultant rather than a company, the arithmetic would be the same but the claim would not: an individual claims the exemption on pay for services performed in the United States on Form 8233, which requires a US TIN and a 10-day waiting period after the form is sent to the IRS, and until those are met the payment is withheld at 30%.
The paperwork does not stop at $0. A US-source payment to a foreign person is reported to the IRS and to the payee on Form 1042-S for the calendar year, with the treaty exemption shown, even when the amount withheld is zero, and the payor files the annual Form 1042 alongside it. The 1099 does not enter the picture for a foreign contractor.
This is the sequence the tool runs for a payment like this one: the rate, the form, and the citation come out the other end.
What a manual calculation requires
Running the four steps by hand for a single payment is feasible. At minimum it requires:
- the payee's W-8, checked for validity and for the treaty claim
- the working-day split for services, or the place-of-use facts for a royalty, taken from the contract or the timesheets
- the current treaty text and, for anything contested, the IRS Technical Explanation
- IRS Publication 515, including the withholding-rate table, to cross-check the article and the rate
- the 1042-S instructions for the income and exemption codes
Each of those sources changes on its own schedule, and a treaty rate looked up in a prior year should be re-verified against the current text before it is reused.
Where the calculation stops being feasible by hand is repetition. Twenty contractors in six countries, paid monthly, with W-8s expiring on different dates, is two hundred and forty determinations a year, each with its own citation. Getting one of them wrong is the payor's liability, because the withholding agent (the paying business) is liable for tax it should have withheld and did not (Internal Revenue Code section 1461).
What a tool does with the same inputs
A withholding determination tool runs the same four steps in the same order. It asks who is being paid and what the W-8 says, where the work was performed and in what proportion, what kind of payment it is, and which treaty and article apply, and it returns the rate, the amount, and the citation. It calculates in minutes what the manual path takes an afternoon to assemble, and it does the part a spreadsheet cannot: it names the article, records the reasoning in an audit memo, and carries the result into the 1042-S worksheet at year end.
The tool does not change the answer. The treaty text decides the rate whether it is read by a person or by software. What the tool changes is the cost of being right on the twentieth payment, and the odds of a citation being on file when the question is asked. Run the four steps for a specific payment and the determination comes out with the citation attached.
Working out what to withhold on a real payment right now?
The tool runs these four steps in this order: who is paid, where the work was done, what kind of payment it is, and what the treaty says. It returns the rate, the form, and the citation for the file.
7 days free, no card, 5 determinations
This article is general information for US withholding agents, not legal or tax advice. Treaty positions turn on the payee's specific facts and the current treaty text. Confirm the analysis for your situation with a qualified tax advisor before relying on it.
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Working out what to withhold on a real payment right now?
The tool runs these four steps in this order: who is paid, where the work was done, what kind of payment it is, and what the treaty says. It returns the rate, the form, and the citation for the file.
7 days free, no card, 5 determinations
This article is for general educational purposes and is not legal or tax advice. Withholding outcomes depend on the specific facts of each payment. Consult a qualified tax professional before making withholding decisions.