In 2011, net payroll tax contributions accounted for 70 percent of total trust
fund income. Net payroll tax contributions consist of taxes paid by employees, employers, and the self-employed on earnings covered by Social Security. These taxes are paid on covered earnings up to a specified maximum annual amount, which was $106,800 in 2011. Table II.B2 shows the tax rates scheduled under current law for 2011.
In 2011, approximately 13 percent of OASDI Trust Fund income came from
reimbursements from the General Fund of the Treasury. Public Law 111-312, the Tax Relief, Unemployment Insurance Reauthorization, and Job Creation Act of 2010, accounts for almost all of the reimbursement for the year. This act specified general fund reimbursement for temporary reductions in revenue due to reduced payroll tax rates for employees and for self-employed workers.
Three percent of OASDI Trust Fund income in 2011 came from subjecting
up to 50 percent of Social Security benefits above specified levels to Federal personal income taxation, and 14 percent of OASDI income came from interest earned on investment of OASDI Trust Fund reserves. The Department of the Treasury invests trust fund assets in interest-bearing securities of the U.S. Government. In 2011, the combined trust fund assets earned interest at an effective annual rate of 4.4 percent. Almost 99 percent of expenditures from the combined OASI and DI Trust Funds in 2011 were retirement, survivor, and disability benefits totaling $725.1 billion. The financial interchange with the Railroad Retirement program was the source of a net payment of $4.6 billion from the combined OASI and DI Trust Funds, which was about 0.6 percent of total expenditures. The administrative expenses of the Social Security program were $6.4 billion, which was about 0.9 percent of total expenditures.
Assets of the trust funds provide a reserve to pay benefits whenever total pro
gram cost exceeds income. Trust fund assets increased by $69.0 billion in 2011 because total income to the combined funds, including interest earned on trust fund assets, exceeded total expenditures. At the end of 2011, the combined assets of the OASI and the DI Trust Funds were 340 percent of estimated expenditures for 2012, down from an actual level of 354 percent at the end of 2010.