Your U.S. filing obligation does not end at the airport.

Brazilian rules look at how you arrive and how long you stay. Someone entering on a permanent visa becomes a tax resident on the day of arrival; someone on a temporary visa becomes one after accumulating a set amount of presence within a twelve-month window; and a Brazilian returning with the intention to stay becomes one on arrival. From that point Brazil taxes worldwide income — which is the moment your U.S. and Brazilian filings start describing the same money. The exact date matters more than people expect, because it splits your year, so it is the first thing we establish.

No. U.S. citizens are taxed on worldwide income wherever they live, so the obligation follows the citizenship and not the address. What changes is everything around it: a second country now has a claim on the same income, reporting of foreign accounts and foreign financial assets becomes live, and the mechanisms that keep the same money from being taxed twice have to be chosen deliberately. Moving adds a filing. It does not remove one.

There is a choice here, and it is not one to make casually. A non-resident spouse can be treated as a U.S. resident for income tax purposes, which allows a joint return — but that election brings your spouse’s worldwide income, including everything earned in Brazil, into the U.S. return, and it stays in force until it is revoked or ends by law. The alternative status keeps their Brazilian income out of the U.S. return and costs something else in exchange. Which one is better depends on what your spouse earns and holds in Brazil. It is arithmetic, not doctrine.

Two different U.S. reports can apply to the same account, and they are not the same form: one goes to FinCEN and covers foreign financial accounts; the other goes to the IRS with your return and covers specified foreign financial assets. Their scopes differ, so an account can fall under one and not the other. On the Brazilian side, a resident holding assets abroad files an annual declaration with the central bank. In practice the same account can be described in three places — and the work is making the three descriptions agree.

It can, and this is where cross-border returns most often go wrong. U.S. law requires certain officers, directors and shareholders of foreign corporations to report that interest — and for U.S. purposes a Brazilian company is a foreign corporation. Whether the obligation reaches you can depend on the filing choice you make about your spouse. A company that is entirely ordinary in Brazil can create a U.S. reporting obligation that nobody mentioned when it was formed.

Brazil and the United States have no income tax treaty in force, so the treaty relief that expatriates in other countries rely on is simply not available here. What remains are unilateral mechanisms inside each country’s own law — a credit for tax paid to the other country, and, for earned income and only when residence or presence abroad qualifies you, an exclusion that has to be claimed on its own form. They work, but they are not automatic and not interchangeable: which one applies depends on the kind of income and on the order in which the two returns are prepared. This is the genuinely technical part, and where the wrong sequence costs money.