US Social Security & Medicare taxes may still apply to what you earn for services performed as an employee or independent contractor outside the US. When do they apply? See the article IRS Social Security Tax Consequences of Working Abroad.
IRS The 3.8% Net Investment Income Tax: information about key planning opportunities and pitfalls presented by the Patient Protection and Affordable Care Act. See specifically #5 "What individuals are not subjected to the Net Investment Income Tax?"
