No. 1: Additional Medicare tax
Normally, all workers pay 1.45% Medicare tax on all of their compensation. Self-employed individuals pay twice that rate: 2.9%. But beginning in 2013, an additional 0.9% Medicare tax applies to Medicare wages and self-employment income that exceed:
• $125,000 if married filing separately
• $250,000 if married filing jointly, or
• $200,000 for any other filing status.
The additional Medicare tax is calculated on your federal tax return. See Form 8959 and its instructions for details.