High Quality Content by WIKIPEDIA articles! For the Old Age, Survivors and Disability Insurance (OASDI) tax or Social Security tax, the Social Security Wage Base (SSWB) is the maximum earned gross income or upper threshold on which a wage earner`s Social Security tax may be imposed. The Social Security tax is one component of the Federal Insurance Contributions Act tax (FICA) and Self-employment tax, the other component being the Medicare tax. It is also the maximum amount of covered wages that are taken into account when average earnings are calculated in order to determine a worker`s Social Security benefit.