This is a common occurrence when somebody has multiple jobs in one year. The employer can't know if you have reached the annual limit. They know to stop when you have hit the maximum for their company, but don't have information on the other jobs. In fact the IRS doesn't let them factor in the other jobs. They have to keep making their payment until you hit the max for their company.
When you fill out the 1040 there will be a line that checks that the total social security amount for each person was not over the annual limit. The extra will be refunded when you file your taxes.
In the future if this happens again you can adjust your withholding to minimize the overage. For the example given in the question to get the 4K extra sooner, increase the number of allowances on the W-4.
- One extra exemption in 2014 was $3950.
- Assuming the 25% tax bracket.
- The exemption is worth 3950*0.25 or $987.50
- assuming 26 paycheck a year (bi-weekly)
- each allowance reduces your withholding by $37.98
- bump the number of allowances by 3 for the last 5 months of the year and get $1139 back early.
You can under withhold federal income tax because you will over withhold social security tax.