What to Expect from the Stock Market

Just about all mainstream personal finance writers advise making stocks the centerpiece of your investment plan. Most will quote a reassuring average market return over a reassuringly long period and make the argument that for sober long-term investors such as yourself, stocks are the place to be. But few writers explain what that long term average return really means and what expectations you should draw from it.

The first thing to understand is that you cannot expect to actually get that average return in any given year. Get Rich Slowly has a guest post by Carl Richards that patiently makes this point with the use of an elaborate animated presentation. His data has an average return of 10% over eighty years and shows that only twice in that time did the actual market return for a year fall between 9% and 11%. I would hope that this is a nearly obvious point to all stock market investors, but I know better.

Moreover, I worry that by saying that the market has good years and bad ones, but that the long run average is high, people are led to believe that as long as they can stick it out through the ups and downs, after twenty years or so they will get the promised average return. This is not necessarily so. Those long run averages are not that much more predictable than individual years.

To illustrate, I will run some numbers of my own. Yale’s Robert Shiller has a website with the S&P 500 index returns annually back to 1871 as well as some other useful stuff such as inflation rates. It turns out that, sure enough, the average return for the US stock market, as measured by the S&P 500, was 10.08% per year over the 138 years from 1871 to 2008 inclusive.

What do we know from this? We know that funds invested in the market on December 31, 1870 and held through December 31, 2008 would have made an average of 10.08% a year. We do not know what the average returns for the next 138 years will be. 10.08% is a pretty solid guess, and in fact is almost certainly the best guess we’ve got, but it’s still just a guess. There is no “true” expected stock market return, even over long periods of time. Setting market return expectations is not science, just thoughtful estimation based on what has happened in the past.

To get a better feel for how volatile even long term averages can be, consider the 80 year period that Richards uses. The 80 year average return for the period ending in 2007 was 11.52%. But move it forward a year to end in 2008 and you get only 10.46%. That is a big difference considering those two periods are 98.75% identical.

And 80 years is a lot longer than the typical person will be invested in the stock market. For most, there is a critical twenty years or so from middle age to retirement when the nest egg does or doesn’t grow. And the returns for twenty year periods are all over the place.

As it happens, the best twenty year period in the stock market since 1871 was recent enough that a lot of us remember it well. From 1979 to 1998 the market averaged 17.32% a year. One dollar invested at the end of 1978 grew to $24.41 by the end of 1998. At the opposite extreme, 1929-1948 averaged only 3.00% a year. The $1 invested at the end of 1928 became only $1.80 by the end of 1948.

There aren’t a lot of people still around who remember the stock market in 1929-1948. But your parents or grandparents might be able to tell you about the period 1962-1981. The market went up an average of 6.57% per year, which doesn’t sound so bad until you find out that inflation averaged 5.50% over the same period, leaving stock investors with an average real return of only 1.07%.

If you are like me, in your mid-forties and heading into the intense period of investing for retirement, the big question is will the period 2009-2028 be more like 1979-1998 or 1962-1981? Nobody knows.

There were 118 twenty year periods ending from 1890 to 2008. The average twenty year period had an average annual return of 9.22%, but a forth of those periods had returns worse than 7% and a fourth beat 11.5%. And you only get to do this once. Consider the difference in circumstances of a person born in 1933, who turned 45 in 1979 and enjoyed fat returns on his way to retirement in 1998 at 65, with somebody born in 1916 whose nest egg went nowhere in the twenty years before his retirement.

What can you do about this? In the most direct sense, nothing. Diversification will help some, but not by as much as you might like. Bad decades for the stock market tend to be bad decades for bonds and real estate too. The truth is that this is one of the many things in life that are beyond your control.

But you can take it into account when doing your financial planning. If the difference between 8% and 10% returns over the next twenty years is the difference between a comfortable retirement and hoping your kids can support you, you need to reconsider your plans. Expecting 10% a year from the stock market over the long run is reasonable, but counting on it is foolish.

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