Having a high income may mean you owe two extra taxes: the 3.8% net investment income tax (NIIT) and a 0.9% additional Medicare tax on wage and self-employment income. Let’s take a look at these taxes and what they could mean for you. 1. The NIIT In addition to income tax, this tax applies on your net investment income. The NIIT only affects taxpayers with adjusted gross incomes (AGIs) exceeding $250,000 for joint filers, $200,000 for single taxpayers and heads of household, and $125,000 for married individuals filing separately. If your AGI is above the threshold that applies ($250,000, $200,000 or $125,000), the NIIT applies to the lesser of 1) your net investment income for the tax year, or 2) the excess of your AGI for the tax...