Count your days wrong and America taxes everything you own

Figures relate to tax year 2025-26 (UK) · 2025 (US)

There is no form to sign and no official to tell you. American tax residence can arrive purely because of how many days you spent in the country, and it reaches people who never applied for anything.

The substantial presence test is a counting exercise spread across three calendar years. Days in the current year count fully, days in the year before count at a third, and days two years back count at a sixth.

Cross the line and America taxes your worldwide income, including your British salary, your ISA and your pension growth. The substantial presence test is the mechanism, and most people who get caught by it never knew it existed.

Key takeaways

• The test counts days across three calendar years, not one.
• Current year days count in full.
• Prior year days count at one third, the year before at one sixth.
• You need 31 days this year and 183 weighted days in total.
• Part of a day in America counts as a whole day.
• Certain visa categories are exempt from counting at all.
• A closer connection claim can rescue you if you qualify.

What is the substantial presence test?

Substantial presence is the day counting rule that decides whether a foreign national becomes an American tax resident. According to IRS guidance, you meet it if you were present at least 31 days during the current year and 183 days across the three year weighted calculation.

Meeting it makes you a resident alien for tax purposes. That status is about tax alone and has nothing to do with immigration, so you can hold a visitor visa and still be caught.

Residence under this rule brings the full American filing regime with it. Worldwide income, foreign account reporting and the rules on British funds all apply from that point.

How does the three year weighting work?

The substantial presence calculation takes every day in the current year at face value. Add a third of the days present in the year before, and a sixth of the days present in the year before that.

If the total reaches 183 and you were there at least 31 days this year, the test is met. The weighting is what catches regular travellers who never spend half a year in any single one.

The arithmetic is simple and the trap is in the look back. Somebody who spends four months a year in America for three consecutive years crosses the line in the third year.

A worked example

The figures below are illustrative. They use round numbers so you can follow each step and substitute your own.

James is British and works for a company with a New York office. He spent 120 days there in 2025, 120 days in 2024 and 120 days in 2023.

His 2025 days count in full at 120. His 2024 days give him 40, and his 2023 days give him 20.

That totals 180 weighted days, which falls just under the line. He is not a resident for 2025 and his British income stays outside the American system.

Had he spent 125 days in 2025 instead, the total would reach 185 and he would be a resident alien. Five extra days would bring his entire worldwide income into charge.

Does a part day count?

Yes, and this surprises people more than anything else about substantial presence. Any part of a day spent in America counts as a full day, so landing at midnight and leaving the next morning gives you two days.

Arrival and departure days both count in full. A weekend trip is therefore three days rather than the two nights you actually spent there.

Over several years of frequent travel that rounding adds up substantially. People counting nights rather than calendar days routinely underestimate their position.

The weighting at a glance

The table shows how each year contributes. Only the first row counts at face value.

Which days do not count?

Several categories drop out of the substantial presence count entirely. Days you were unable to leave because of a medical condition that arose while you were there do not count, nor do days commuting from Canada or Mexico on a regular basis.

Days in transit also drop out where you spend less than 24 hours between two foreign points. Changing planes in Chicago on the way to Mexico is not a day in America.

Crew members of foreign vessels are excluded while working in that capacity. Each exclusion has conditions and some require a form to claim them.

Who counts as an exempt individual?

Certain visa holders ignore their days completely for substantial presence, which differs from the days themselves being excluded. Students on F, J, M or Q visas and teachers or trainees on J or Q visas fall into this group.

Foreign government related individuals and certain professional athletes are also exempt. The exemption usually runs for a limited number of years rather than indefinitely.

Claiming it requires filing a form even when no tax is due. Students often discover this years later, having assumed the status was automatic.

What is the closer connection exception?

It lets you escape residence despite meeting substantial presence, provided you were present under 183 days this year alone and can show closer ties to another country. Your home, family, belongings and accounts all feed into that judgement.

The exception looks at where your home, family, belongings, bank accounts and social ties sit. Somebody with a British house, a British family and a British life has a strong claim.

Our guide to the closer connection exception covers how to make it. It fails automatically if you spent 183 days or more in the current year.

Can the treaty help instead?

It can, where you are resident in both countries under their domestic rules. The treaty tie-breaker then allocates residence to one country based on permanent home, centre of vital interests and habitual abode.

A tie-breaker claim is a formal position that goes on a return with a disclosure. It is not something that happens silently, and you still file.

Our guide to Form 8833 treaty positions covers the disclosure. The treaty route works even where you exceeded 183 days in the current year.

What happens if you meet it?

Meeting substantial presence makes you a resident alien, taxed on worldwide income from your first day of presence that year. Your British salary, interest, dividends and gains all enter the American calculation.

The reporting obligations arrive with it. Foreign account reports for every British account, disclosure of British funds under the PFIC rules and reporting of any British company you control.

Foreign tax credits usually stop you paying twice on the same income. They do nothing about the compliance burden, which is the real cost.

Does the first year work differently?

It can. Where you become resident part way through a year, your residency starting date is generally the first day you were present in that year, which can create a dual status return.

There are elections that change this, including one that treats you as resident for the whole year. Whether that helps depends entirely on the shape of your income.

Our guide to the first year choice election covers the options. The decision is easier before the year ends than after.

How do you prove your day count?

With a record kept as you travel rather than one rebuilt afterwards. Boarding passes, passport stamps, calendar entries and card transactions all help. A substantial presence calculation that rests on memory tends to fall apart under scrutiny.

Passport stamps alone are unreliable because electronic gates often skip them. Airline records and bank statements fill the gaps more reliably.

Keep a running count each year rather than rebuilding it in April. The exercise takes minutes if it happens as you travel.

Does it apply to Americans in Britain?

No. An American citizen pays tax on worldwide income wherever they live, so day counting changes nothing for them. The substantial presence test exists to catch foreign nationals, which in this context means British citizens spending time in America.

Substantial presence matters to British citizens and other foreign nationals who spend time in America. It is the mechanism that turns a frequent visitor into a taxpayer.

It also matters to Americans employing British staff who travel. The employer often discovers the problem before the individual does.

What about state taxes?

States run their own residence rules and ignore the federal test entirely. New York and California use their own day counts and domicile concepts, so substantial presence tells you nothing about whether a state considers you resident.

So you can escape federal residence under a treaty claim and still be a state resident. The two questions are decided separately.

Our guide to US state tax for expats covers the state position. It is the part most advisers forget.

What if you are posted to America for a year?

Then you will almost certainly meet substantial presence in that year, because a twelve month posting puts you well past 183 days on current year days alone. The closer connection exception closes to you at that point.

The treaty tie-breaker becomes the route worth exploring instead. Where your permanent home and family remain in Britain, the treaty can still allocate residence here.

Our guide to a US secondment covers the wider assignment position and the payroll side.

Does the test affect your family?

Each person counts their own days, so a spouse who travels less may escape entirely. Children count separately too, though they rarely hold income that matters. One household can therefore split across two tax systems.

That can produce a split household, with one spouse a resident alien and the other not. Filing jointly then requires an election that brings the non-resident spouse into the American system voluntarily.

Our guide to a nonresident alien spouse covers that election and when it makes sense.

What about days you spent working remotely?

Physical presence is what counts, not what you were doing. A day spent working for your British employer from a hotel in Boston is a day in America for substantial presence purposes.

The nature of the work matters separately, because days worked there can create American source employment income even below the residence threshold. Those are two different questions about the same trip.

Holiday days count exactly the same as working days. The rule does not care why you were there.

Can you lose residence once you have it?

Yes, by failing the test in a later year. Residence under this rule is tested annually rather than once, so cutting your travel brings you back out of the American system without any formal application.

The year you leave can produce a dual status return, splitting the year at your residency termination date. Establishing that date properly matters.

Our guide to the dual status tax return covers how the split works in practice.

Does it matter which years you count?

Calendar years, always, regardless of the British tax year ending in April. The substantial presence calculation runs on the American year alone, which catches people who track their travel against the British one out of habit.

That mismatch catches people who track travel against the British year out of habit. Days in February and March sit in different years on the two calendars.

Keep the running total on a calendar year basis from the start.

What does it cost to get wrong?

Several years of unfiled American returns, foreign account reports and possible penalties for each. The returns themselves usually produce little tax, because British rates are higher and credits absorb the liability.

The exposure sits in the information returns rather than the tax. For 2025 the foreign account reporting threshold stays at $10,000 across all accounts combined, and a non-wilful failure to file can carry a penalty of around $10,000 per account for each year missed.

Our guide to streamlined filing covers the catch-up route where this has already happened.

How to apply the test

1. List every calendar day you were physically in America this year.
2. Count arrival and departure days as full days.
3. Repeat the exercise for the two previous calendar years.
4. Multiply last year's days by one third.
5. Multiply the year before by one sixth.
6. Add the three figures together.
7. Check whether the total reaches 183 and this year reaches 31.
8. If it does, consider the closer connection or treaty routes.

Mistakes and penalties we see with day counting

The first is counting nights instead of days. A four night trip is five days under this rule and the difference compounds across a year of travel.

The second is ignoring the two earlier years. People look only at the current year, see well under 183, and assume they are safe.

The third is assuming a visitor visa protects you. Immigration status and tax residence are separate questions with separate rules.

The fourth is claiming the closer connection exception after spending 183 days or more in the current year. The exception is simply unavailable at that point.

How US UK Tax Accountants helps

We rebuild your day count properly, apply the weighting across all three years, and tell you where you stand before the year ends rather than after. Where you are close to the line, a few days of travel planning can change the outcome entirely.

Where the test is already met, we look at the closer connection exception and the treaty route. Our treaty relief service covers both positions and the disclosures they need.

If you travel to America regularly for work, get in touch before the end of the calendar year. After 31 December the count is fixed.

Last reviewed 11 October 2026. This article is general information and not personal tax advice. Every travel pattern turns on its own facts, so take advice on yours before relying on a count.