Two great options are the SPDR S&P 500 ETF Trust (NYSEMKT: SPY) and the iShares U.S. Healthcare ETF (NYSEMKT: IYH). Both funds have averaged a compound annual growth rate of about 15% in recent years, and so that's the assumed percentage I'll use for the purpose of these calculations. Investing right now, with the markets at all-time highs, could mean lower future returns, especially if inflation rates rise in the next few years and that leads to some pullback in stock prices.