Is monthly federal withholding tax on Social Security benefits calculated on the full benefit amount or on the amount remaining after the premium for Medicare Part B is deducted? For example, if my full benefit is $1,000 and I elect 10 percent withholding, is my monthly tax $100 ($1,000 x .10) or $86.60 ($1,000 - $134 = $866 x .10)? Many thanks.
I'm sorry, but I can't give you a definite answer. I thought that the withholding was based on the gross amount before other deductions, but I recently received a question from another reader that indicates the withholding is based on the net amount. Social Security's website isn't clear on this subject (https://www.ssa.gov/planners/taxwithold.html), so I'm afraid you'll need to check with Social Security for an answer.