This chart shows what happens when you hold stocks for decades

If you're a long-term investor, you shouldn't necessarily be worried about a crash in the near term.

Nobel laureate Robert Shiller maintains a collection of monthly historical-price data for the S&P 500 and related older stock indices going back to 1871.

To see the effects of holding stocks for the long run, we looked at what an investor's price return would have been if they bought the equivalent of an S&P composite-index fund in each month and then held it for 10, 20, 30, or 40 years after that month.

Business Insider/Andy Kiersz, data from Robert Shiller

Over the course of the twentieth century, in most periods, the longer you held stocks, the better your price return. One exception fell between late 1968 and early 1971: Thirty years after that time interval captured the end stages of the dot-com bubble of the late 90s, while forty years later fell in the midst of the financial crisis and Great Recession, leading to a higher 30-year than 40-year return.

A similar pattern can be seen comparing 20- and 30-year returns in the late 70s and early 80s, and 10- and 20-year returns in the late 80s and early 90s.

And the message is pretty simple: stocks usually go up.