When does a green-card holder start being taxed on worldwide income?

Under the IRS green-card test, you're a resident alien for tax purposes from the first day you're present in the U.S. as a lawful permanent resident, and from that day the U.S. taxes your worldwide income, not just U.S. earnings. This status continues every year you hold the card until it's officially revoked or abandoned, even if you spend time abroad. Simply living outside the U.S. does not end U.S. tax residency for a green-card holder. That means foreign interest, dividends, rent, and capital gains all become reportable, and you may owe extra information filings like the FBAR. The IRS explains the green-card test in Publication 519 at irs.gov.