Calculating your basis, or the combination of cash paid plus any dividends reinvested that have already been taxed, is no easy task.

First, find the purchase date (or dates, if you bought the fund or stock over a period of time) and price (or prices). Next, find out how much of your gain has already been taxed as dividends (assuming that you've reinvested those dividends in the stock or fund) for each year since you've owned the security. The difference between the value of the investment today and the basis is your capital gain.

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