Think in layers
Federal tax rules compare a combined-income measure with filing-status thresholds. Other income—including some tax-exempt interest—can cause part of Social Security benefits to be included in taxable income. The included amount then becomes part of the ordinary tax calculation.
Plan withdrawals together
Before taking a large IRA withdrawal, capital gain, or Roth conversion, estimate how it interacts with Social Security. A one-dollar increase in another income source can affect more than one line of the return, so use tax software or a professional for the final filing decision.