Every 40-year Returns Curve from US Stock Indexes since 1870, superimposed by Zoni Nation
This image represents all possible return curves from index funds 1870 to 2016, using a buy-and-hold strategy. All values are "real" returns, meaning that dividends and inflation have already been accounted for.
Values are done on a "cash multiplier" basis, meaning the initial investment has been summarized as a single factor which describes your return. The black line is the exact average from month to month (not a regression line). Average doubling time for index investors is roughly 10 years.
Note that all curves stabilize over a 40-year period to turn a profit. This assumes you buy an index and then hold until retirement.
The data was taken from Robert Shiller, combined with more recent data from the S&P500 and plotted in R/ggplot2.
For more information, read here: https://github.com/zonination/investing/blob/master/README.md