From today’s level, I’d take the under on 7.5%. Over time, there are several reasonably good indicators to view prospective returns. For example, the market value of the equity market as a percentage of GDP has been a good guidepost. That metric has never been higher, and implies negative returns over the intermediate term. Of course, rates have never been lower, either, but low rates also give rise to low prospective absolute returns.
All of this is at current prices. Last April was a very different story. So, if you consistently invest over time relatively equal increments, you should benefit from pullbacks and lower prices. Thus, you may do better but I still think 7.5% will be tough.
Buying stocks is investing in businesses, and over the long run, the performance of the business will determine returns. However, even spectacular business performance can’t overcome an inflated valuation. I’ve always thought it easier to evaluate earnings yields, simply the inverse of a P/E ratio. Think of the P as the price you are paying for all of the dollars and capital invested in a business. If you started the business yourself, you would have book value and historical cost as your “P.” For stocks sporting incredibly high P/E ratios, or meager earnings yields, the questions that need to be considered is how long will it take for the business to grow such that you have a reasonable yield on your acquisition price, and how confident are you that the business will grow to that level? Basic questions often rip apart valuations. Tesla is the easiest to do.