The health care legislation enacted in 2013 included a new tax that was designed to affect upper income taxpayers. The 3.8% tax is imposed ONLY on those with more than $200,000 of Adjusted Gross Income (AGI) ($250,000 on a joint return). The tax applies to investment income, defined as interest, dividends, capital gains and net rents. These items are all included in an individual's AGI. A formula will determine what portion, if any, of these types of investment income would be subject to the tax.
The tax is NOT a transfer tax on real estate sales and similar transactions. Not long after the tax was enacted, erroneous and misleading documents went viral on the Internet and created a great deal of misunderstanding and made the tax into something far more draconian than the actual provisions.
The new tax does NOT eliminate the benefits of the $250,000/$500,000 exclusion on the sale of a principal residence. Thus, ONLY that portion of a gain above those thresholds is included in AGI and could be subject to the tax.