Because it is taxable income in the year you receive it. The amount will be taxed at the capital gains rate, but it should still show as income in the summary screens. the amount of capital gains is added to your Adjusted Gross Income and can cause changes in other things in your return that are based on AGI, such as itemized deductions for medical expenses, some credits with AGI limits, or real estate losses. Even though it is taxed at a different tax rate, it's still part of your AGI.