Okay, here is an updated version of a post I did a couple of years ago where I took the returns for the S&P and analyzed them by various rolling-periods (5-years, 10-years, and 20-years). Today, I want to look at 20-year rolling-period returns. Check out the graphic I prepared (*you can click on the graphic to see a larger version):*

It’s incredible just how skewed results can become due to one bad or good year. Notice how 2008’s -37% return dropped the average annual return over the last 20 years to 5.60% (note that these returns include inflation).

Here are some other interesting findings:

• **0** The number of 20-year periods that had a negative return.

• **64** The number of periods that had a positive return.

• **403.02%** The average TOTAL return of all the 20-year periods.

• **$50,302** The average amount (after inflation) that $10,000 grew to over each 20-year period.

• **$130,946** The most $10,000 would have grown to during a 20-year period.

*• $11,082 The smallest amount that $10,000 would have become over each 20-year period.
*

I think you meant to say “20-year period” instead of “5-year” period for the average/most/smallest that $10,00 would’ve grown to. Otherwise a good write-up. Any chance you can give us the average compound return for the entire dataset — I think this number has historically been 9% or so.

Through 2008, the average annual rate of return on the S&P is 9.62% or 7.18% adjusted for inflation.

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Its kind of amazing how bad the market was betweeen 1955-1993, considering that much of this time the economy was growing quickly, and the middle class were doing very well. Inflation adjusted the market never broke 5.17% (only once) and usually was in the 1-2% inflation adjusted range. I can see why people thought equities were dead in the late 80’s. Considering the ‘conservative assumptions’ of today-say 5% inflation adjusted, if you started work in 1955, you would have been in serious trouble at retirement.

Would love to see the numbers through 2009 when available! Might cheer some of us up a little.