A household employer only has to pay social security and Medicare taxes only on cash wages paid to an employee that exceed the threshold amount for the year.
If the amount paid is less than the threshold, no social security or Medicare taxes are owed.
If social security and Medicare taxes must be paid, you will need to file Form 1040, Schedule H
(PDF), Household Employment Taxes.
You must withhold the employee's portion of the social security and Medicare taxes unless you choose to pay both the employee's share and the employers share. The taxes are 15.3% of cash wages. Your share is 7.65% and the employee's share is 7.65%.
You may also be responsible for paying federal unemployment taxes, reported on Form 1040, Schedule H.
You and your employee may agree for you to voluntary withhold income tax from wages paid to the employee, reported on From 1040, Schedule H.