Refund of Excess Withholding
The Social Security tax only applies to a limited portion of your earned income for the year -- any earned income above that threshold isn't taxed. However, if you work for multiple employers, you may have excess funds withheld because neither employer knows how much the other is withholding. For example, in 2015, the cap is $118,500. If you earned $100,000 from one employer and $50,000 from another, and both employers withheld Social Security taxes on your entire salary, you would have had Social Security taxes withheld on $150,000, which is more than the $118,500 cap. You can claim the excess withholding as a credit on your federal income tax return.