Do I need international, developed-market, and emerging-market funds, or just U.S.?

You don't strictly need international funds, but most diversified investors hold some — the U.S. is roughly 60% of global stock value, so a U.S.-only portfolio skips the other 40%. International splits into developed markets (Europe, Japan, Canada, Australia) and emerging markets (China, India, Brazil, and others), which carry higher growth potential and higher volatility. The simplest approach is one total-international fund that holds both, often 20%–40% of your stock allocation. International stocks don't always move with the U.S., which can smooth your ride and has historically led during some decades. If you're an immigrant or NRI with ties abroad, factor in currency and any home-country exposure you already have. Set a target split at wealthserene.com/tools/portfolio-builder.