Capital Gains Tax. Stephen is in a 10 percent marginal tax bracket in 2018, he sold stock that he had heid for nine months for a gain of $2,100. How much tax must he pay on this captal gain? How much would the tax be if he had held the stock for 17 monks? The amount of tax he must pay on this captal gain is 5 (Round to the nearest dollar) It he had heid the stock for 17 months, the tax would be 5 (Round to the nearest dollar)