The Additional Medicare Tax goes into effect for taxable years beginning January 1, 2013. An additional tax of 0.9 percent applies to individuals' wages, other compensation and self-employment income over certain thresholds (see below table).
There is no requirement that an employer notify its employee when the business begins withholding Additional Medicare Tax. The employer is required to withhold Additional Medicare Tax on total wages, including noncash fringe benefits, in excess of $200,000. There is no employer match for Additional Medicare Tax.