Social Security Taxes and Wage Limits
There is a limit on the amount of wages that are taxed for Social Security, but there’s no limit on the wages that are taxed for Medicare.

Social Security Taxes
Your employer must withhold 6.2% of your income for old age, survivor, and disability insurance through Social Security, up to a maximum income of $87,900 for 2004 and $90,000 for 2005. The income ceiling rises every year.

Medicare Taxes
Your employer must withhold 1.45% of all your wages, without any income limit, for hospital insurance under Medicare.