It's tempting to think of 'NRI' as a single, portable status — either you are one or you aren't. In reality, India and the US each run their own residency test, on their own facts, for their own tax year. It's entirely possible to be a non-resident for Indian tax purposes and a tax resident of the US in the very same year, or the reverse during a transition year like the one you move.
That matters because residency, not citizenship or visa category, is usually what determines which country taxes your worldwide income versus only your India-sourced or US-sourced income.
How India decides
India's residential status test is based primarily on the number of days you're physically present in India during the financial year (and the preceding years), with different day-thresholds depending on whether you're an Indian citizen or person of Indian origin visiting India. Cross the relevant threshold and you may be classified as 'Resident and Ordinarily Resident,' 'Resident but Not Ordinarily Resident (RNOR),' or 'Non-Resident,' each with different consequences for what income India taxes.
A Finance Act 2020 change added an extra wrinkle for higher-income visiting NRIs: a shorter 120-day threshold can apply in certain cases. Our residency calculator on the DTAA & Tax Residency page walks through this day-count and flags when that nuance applies to you.
How the US decides
The US uses a different mechanism entirely for non-citizens: the Substantial Presence Test, a formula that weighs your days present in the current year against a fraction of the two preceding years. Meet the threshold and the IRS treats you as a US tax resident for that year, generally taxable on worldwide income, regardless of visa type.
Green card holders and US citizens are treated as US tax residents automatically, independent of the Substantial Presence Test, for as long as that status is held.
When both countries claim you
Dual residency in the same year is possible, and it's exactly the situation the India-US Double Taxation Avoidance Agreement (DTAA) exists to resolve — through 'tie-breaker' rules and relief mechanisms like foreign tax credits, so the same income isn't taxed twice at full rates in both countries.