Social Security taxation basics

Up to 85% of Social Security benefits may be included in federal taxable income, depending on “combined” or provisional income. That measure generally includes AGI, nontaxable interest, and half of Social Security benefits.

Withdrawals from traditional IRAs and 401(k)s, and Roth conversions (which add to taxable income), can push provisional income higher and increase the taxable portion of benefits. That interaction is separate from Medicare IRMAA, but both are income-sensitive — so stacking them without looking at the math is a common planning blind spot.

Large consumer calculators sometimes omit state tax, IRMAA, or benefit taxation. When a tool omits a variable, the omission should be explicit. Our Gate 0 tool focuses on IRMAA arithmetic only and does not claim to compute your full tax return or benefit taxation.

For official definitions and worksheets, start with IRS Publication 915 and SSA materials. This page is a map, not a filing guide.