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URL:  http://boards.fool.com/the-actual-return-in-this-situation-gets-very-30251915.aspx

Subject:  Re: Finding a good calculator Date:  9/9/2012  12:04 AM
Author:  pauleckler Number:  24935 of 25214

The actual return in this situation gets very complicated. I would suspect that a precise calculation is more trouble than it is worth.

However, if you made 12 equal monthly contributions to the account and took no distributions, you can approximate the sum of those by treating the accumulating value as a triangle.

So suppose the account is worth $10K on Jan 1 and you make contributions of $100 per month. At end of the year cost basis is $11200. Your total gain is final value of the account minus $11200. I would calculate return as total gain X 100/(10,000 + 6x100). This is approximate but not too complicated.

You can do a more detailed calculation using the number of shares purchased each month and 11/12 year as the time for January's investment, 10/12 for Febs, . . . , 0/12 for Decembers.

Of course for large accounts, the contributions may not matter so much and can probably be ignored. For small accounts the first approximation works well enough.

You mention expenses, but that does not directly affect the calculation. Its all about your investment and final value at end of the year.
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