Final answer:
High-income taxpayers may have up to 85% of their Social Security benefits included in their taxable income, depending on their total income. This percentage is based on income thresholds that determine the taxable amount of Social Security benefits.
Step-by-step explanation:
For high-income taxpayers, a significant portion of Social Security benefits may be included in their taxable income. Generally, individuals with a higher total income will have a larger percentage of their Social Security benefits subject to income tax. For example, if you are filing as an individual and your combined income ('combined income' refers to your adjusted gross income plus nontaxable interest plus half of your Social Security benefits) is above $34,000, up to 85% of your Social Security benefits may be taxable. The specific thresholds can change, so it is important to check for the most recent tax year or consult a tax professional for an accurate figure.