Some taxpayers have to pay federal income taxes on their Social Security benefits. This usually happens only if you have other substantial income (such as wages, self-employment, interest, dividends and other taxable income that must be reported on your tax return) in addition to your Social Security benefits.
No one pays federal income tax on more than 85% of his/her Social Security benefits based on IRS rules.
Generally, if your "combined income" is more than $25,000 ($32,000 if married), then Social Security will be taxable (either 50% or 85%)
Navigate to Federal Form 1040 line 5a Social Security benefits (5b is the taxable portion).