The major changes to Form 941 are on lines 5a through 5f. The Social Security (OASDI) tax rate on lines 5a (Taxable Social Security wages) and 5b has increased from 10.4% to 12.4%. The 2% increase is due to the expiration of legislation that temporarily reduced the employee Social Security tax rate from 6.2% to 4.2% through Dec. 31, 2012.
Line 5d, Taxable wages & tips subject to Additional Medicare Tax withholding, has been added to Form 941. Beginning in 2013, in addition to withholding Medicare tax at 1.45%, employers must withhold an additional 0.9% Medicare tax from wages paid to an employee in excess of $200,000 in a calendar year. Employers must begin withholding the additional Medicare tax in the pay period in which wages are in excess of $200,000, and continue to withhold it until the end of the calendar year. The tax is only imposed on employees. All wages that are subject to Medicare tax are also subject to additional Medicare tax withholding if paid in excess of the $200,000 withholding threshold.
There are still lines on the 2013 Form 941 for COBRA premium assistance payments/subsidy (lines 12a and 12b) because some involuntarily terminated workers may still be eligible to receive a COBRA premium subsidy, even though the subsidy was not available to most workers beyond Aug. 31, 2011.