Social Security is funded by a payroll tax of 12.4 percent on eligible wages — employees pay 6.2 percent and employers pay the other 6.2 percent (with self-employed workers paying the entire 12.4 percent). For 2021, the maximum amount of earnings subject to the Social Security tax will increase to $142,800 from $137,700. The money paid in by today's workers goes to cover current benefits, with any excess going into the Social Security trust fund.