OCI (Overseas Citizen of India) and PIO (Person of Indian Origin, a scheme largely folded into OCI) are immigration and civil-status categories — a foreign citizen of Indian origin holding one is explicitly not an Indian citizen (India doesn't recognize dual citizenship), and the card itself confers travel and residency-type privileges, not a tax classification. It's a common and understandable mix-up: OCI cardholders sometimes assume their Indian tax treatment simply follows from the card, when in fact India's tax residency is worked out independently, on the Income Tax Act's own day-count tests, for every individual regardless of OCI status.
Where OCI/PIO status does interact with the tax rules
The interaction isn't nothing, though — it's narrow and specific. The Finance Act 2020 shortened-threshold rule (the 120-day residency trigger for visiting individuals with India-sourced income above the commonly cited Rs 15 lakh mark) is written to apply to "a citizen of India or a person of Indian origin," meaning OCI/PIO status is exactly the hook that pulls a foreign-citizen visitor of Indian origin into that shorter day-count, rather than the general 182-day threshold that would otherwise apply to a visiting foreign national with no such origin. In that one place, the civil-status label genuinely does matter for the tax outcome — it's just not itself the tax status. This site's own residency calculator flags this nuance when the visiting-citizen/PIO box is checked.
On the US side, it's simpler: it doesn't come up at all
OCI/PIO status has no bearing on US tax residency, which is decided entirely independently through the Substantial Presence Test, green card status, or US citizenship. A US citizen who also holds an OCI card is a US tax resident purely on citizenship — the OCI card changes nothing about that determination, in either direction.
A related, narrower provision worth not conflating
Separately, Finance Act 2020 also introduced a "deemed resident" rule for Indian citizens with more than Rs 15 lakh of non-foreign-source income who aren't liable to tax anywhere else by reason of domicile or residence, aimed at closing a "stateless income" gap. Multiple sources describe this specific deeming provision as restricted to Indian citizens — not extended to OCI/PIO holders — which is the opposite direction from the 120-day rule above (that one explicitly includes PIOs; this one doesn't). Given how easy the two provisions are to conflate, and how much recent legislative attention this area has gotten, this is worth confirming directly against the current Income-tax Act text or with a CA rather than taken as settled from this summary alone.