Shareholders who wish to make a charitable donation can come out ahead by giving away some of their stock in a forced sale, such as InBev's purchase of Anheuser-Busch Cos., according to an example provided by Greater St. Louis Community Foundation.

The example assumes that a shareholder has 10,000 A-B shares, with an average cost basis (what the shareholder paid for the stock, adjusted for splits) of $5 a share, and she sells at InBev's offer price of $70 a share. The shareholder itemizes deductions and has a combined income tax rate (federal and state) of 35 percent. Her shares are subject to long-term capital gains tax of 20 percent (combined federal and state tax.)

She sells 6,500 shares at $70 a share or $455,000. Subtracting her cost basis of $32,500, her capital gain is $422,500. She pays taxes of $84,500 on the gain.

She also gives the remaining 3,500 shares to charity, which sells them for $245,000. She gets a tax deduction of $85,750. The deduction more than offsets the capital gains tax she paid on the sale, leaving her with $456,250.

If, on the other hand, she sold all 10,000 shares, she would have a capital gain of $650,000, resulting in capital gains tax of $130,000. To offset that gain, she would have to make a cash donation of $372,000. That would leave her with $328,000 after taxes.

The numbers have been rounded to simplify the examples.