Can I build a fully diversified portfolio using only fractional shares?

Yes, and that's one of the best things about them. Fractional shares let you buy a precise dollar amount of a stock or ETF regardless of its share price, so with as little as a few dollars you can own slices of many holdings and stay fully invested with no idle cash. This makes it easy to build a diversified, dollar-cost-averaged portfolio on a small budget and to put every contribution to work immediately. The main things to watch are your brokerage's specific fractional policies, potential complications when transferring accounts, and the temptation to over-collect too many holdings you can't track. A simpler path is buying fractional shares of one or two broad index ETFs, which delivers instant diversification. Use the Portfolio Builder at wealthserene.com/tools/portfolio-builder to design an allocation before you buy.