County College of Morris is an equal opportunity and affirmative action institution and complies with Title IX, ADA and Civil Rights obligations. Quicklinks Academic Advisement
Determining Taxable Amount. If your base income exceeds the limit for your filing group, you'll have to pay taxes on some of your Social Security benefits. If you're a single filer and your base income is between $25,000 and $34,000, you'll have to pay tax on up to 50 percent of your Social Security benefits.
Calculation. To calculate Social Security tax withholding on 401(k) contributions, your employer first determines your gross wages for the pay period. Gross wages are your earnings before deductions. Your employer subtracts Social Security tax from your gross wages and then deducts your 401(k) contribution.For example, you earn $450 for the weekly pay period and elect 6 percent toward your 401(k) account.pecifically, if Social Security tax applies, so does Medicare tax. Your 401(k) contributions are subject to Medicare tax of 1.45 percent, as of 2012.