Have you bought stock in a company that later dropped in value? While you may prefer to forget such an ill-fated investment, at least you can claim a capital loss deduction on your tax return. Here are the rules that apply when a stock you own is sold at a loss or becomes completely worthless. Stock sales produce capital losses  Stocks are capital assets and produce capital gains or losses when they’re sold. Your capital gains and losses for the year must be netted against one another in a specific order, based on whether they’re short-term (held one year or less) or long-term (held for more than one year). If, after netting, you have short-term or long-term losses (or both), you can use them to offset up to...