If I move back home and take an early 401(k) or IRA withdrawal as a nonresident, how much tax will I owe?

Expect a meaningful bite. As a nonresident alien, the plan generally withholds a flat 30% on the distribution unless a tax treaty between the U.S. and your country lowers that rate, India's treaty, for example, can reduce withholding on certain pension-type distributions. On top of withholding, if you're under 59½ a 10% early-withdrawal penalty usually applies. So a $50,000 early withdrawal could lose $15,000 to withholding before penalties. Your home country may also tax the same money, though a treaty and foreign tax credits can ease double taxation. Because the rules turn on your specific treaty and account type, get the treaty article number right before withdrawing. Often it's cheaper to leave the money invested. See wealthserene.com/for/nri-returning-to-india.