Excluded days reduce countable days before weighting
Roam Window calculates each year's countable total as physical-presence days minus excluded days, then applies the full, one-third, or one-sixth weight. The order matters. An excluded current-year day removes six sixths from the exact numerator, a first-prior-year day removes two sixths, and a second-prior-year day removes one sixth.
That exact subtraction does not decide whether the day belongs in the excluded column. The form deliberately asks for a number the user has independently determined. It does not ask the factual questions needed to classify commuting, transit, vessel-crew, medical-condition, NATO, teacher, trainee, student, athlete, or other circumstances discussed in IRS materials.
The IRS categories have different conditions
The IRS substantial presence page identifies regular commuters from Canada or Mexico, certain transit under 24 hours, crew members of foreign vessels, people unable to leave because of a medical condition that developed while in the United States, and exempt individuals. Publication 519 supplies further definitions and limitations. The same label can depend on timing, purpose, status, and conduct.
The term exempt individual is especially easy to misunderstand. The IRS explains that it refers to specified categories for presence-day counting; it is not a general statement that the person is exempt from US tax. Because the category can involve visa-related and factual requirements, the estimator never turns a selected label into an eligibility decision.
Form 8843 is a separate procedural question
The IRS says that a person excluding presence days as an exempt individual or because of a medical condition that developed in the United States must file Form 8843 with an income tax return, or send it to the address in the instructions by the return due date when no return is required. If the person does not timely file Form 8843, the IRS says the person cannot exclude the days, unless clear and convincing evidence shows reasonable actions to learn the filing requirements and significant steps to comply.
If Form 8843 may be relevant, open the current IRS form page and Publication 519 for the year being reviewed. Forms and instructions can change. Keep the official form workflow separate from the calculator: Roam Window does not generate, transmit, store, or file Form 8843, and it does not collect the medical or status details that may appear in that process.
A careful excluded-day workflow
First total every calendar day of physical presence. Second, list each proposed excluded day with the category and official source reviewed outside Roam Window. Third, confirm any connected procedural step independently. Only then transfer the annual excluded totals into the calculator. This workflow prevents a plausible-looking percentage from hiding an unsupported subtraction.
After calculation, read the explanation row for each year and confirm that physical minus excluded equals countable. Retain exact fractions in the weighted total. If any excluded-day classification changes, update the relevant year's excluded total and recalculate. The new output reports the revised formula gates only; it still does not establish eligibility, filing status, or any final tax outcome.
- Do not treat an IRS category name as automatic eligibility.
- Review Form 8843 separately when the IRS materials connect it to the facts.
- Recalculate whenever an excluded-day decision changes.
Official sources
- IRS — Substantial presence test and excluded days
- IRS — About Form 8843
- IRS — Publication 519, U.S. Tax Guide for Aliens
Sources were checked on . Linked institutions may update their guidance after that date.