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Ed: Now updated with initial February 2015 data!  (Per Shiller: As of 2/13 close.)

Below is a calculator with a benefit not seen on any other calculators Ive seen online one which includes dividend reinvestment.  It uses data from Robert Shiller, available here .

We also present this data from the perspective of average return over various time periods; you can find that calculator here.   A Treasury Return Calculator using the same data can be found at that link.  For a complete list of all our calculators, for investing and otherwise, go to this page .

The S&P 500 Dividends Reinvested Price Calculator (With Inflation Adjustment)

One issue you run into a lot when you are discussing optimal savings strategies is the inability of people discussing their returns versus the S&P 500 to produce a fair comparison. They will say, for example, that the S&P 500 index was at the same level as it was at some time in the past so therefore investing in the index was a waste of time.  Heres the key to this calculator:

• S&P 500 Index Return — The total price return of the S&P 500 Index. So if it is at 1000 on the start and end date, this will be 0.
• S&P 500 Index Annualized Return — The total price return of the S&P 500 index (as above), annualized. This number basically gives your return per year if your time period was compressed or expanded to a 12 month timeframe.
• S&P 500 Dividends Reinvested Index Return — The total price return of the S&P 500 if you had reinvested all of your dividends.

• S&P 500 Dividends Reinvested Index Annualized Return - The total price return of the S&P 500 if you reinvested dividends. Again, it will annualize the return given above.
• Inflation Adjusted (CPI)? - Whether the calculation you did is using CPI adjusted values provided by Shiller, or showing return before inflation. Hit the checkbox above the buttons to turn on or off the inflation adjustment.

Methodology

Professor Shiller lists his methodology on his site all values internal to this tool use the values he provided.  One thing to note is that the months Price isnt the price on a particular day, but an average of closing prices based on a years quarters data.  Its best to look at it like what did the average investor who invested randomly during the beginning month and sold randomly during the ending month do?.

To calculate the dividend reinvested price index, I take the dividend yield reported in any month of Shillers data and divide by 12 to get an approximate count of dividends paid out in the month. Using that number, I calculate how many shares of the S&P 500 index I can buy, and run a cumulative count from 1876 to 2012. Is this completely fair? No, but it would be nigh impossible to go back and calculate exact S&P 500 payout dates and figure out what the index was trading at on that date. Deal with it.

Also, transaction fees and management costs arent included, which would come out of a real investors return.

Implications

Does it mean a lot to include reinvested dividends? Well, yes. Consider the following in July 1999 Shillers data has the S&P 500 at 1380.99. In April 2012? 1386.43. If you only used the price return of the S&P 500 youd appear to have made a .394% gain, when, dividends reinvested, it was more like a 26.253%% gain. It seems shabby, but the effect is much more pronounced over longer periods of time. Consider from January 1950 until April 2012 the return was 8,182.464% for the index price and a whopping 66226.545% for the dividends reinvested index. In short? Since 1950, roughly 89% of your gains would have come from reinvesting your dividends. Still think its shabby?

Thank Yous

To Robert Shiller, of course, for posting his data publicly.