If your tax bill was higher than anticipated, it could be due to the Net Investment Income Tax (NIIT). NIIT is a tax on investment income, such as interest, dividends, and capital gains. Importantly, it is a 3.8% surtax, meaning it is an extra tax on top of other taxes that may be owed on your investment income. For instance, qualified dividends and capital gains are generally taxed at 15%, but the rate for those subject to the NIIT will essentially be 18.8%. NIIT only applies if your modified adjusted gross income (MAGI) is more than a certain threshold – $200,000 (single taxpayer) or $250,000 (joint taxpayer). This is not a new tax – it has been in effect since 2013! Continue reading for more details.
https://www.bankrate.com/investing/net-investment-income-tax-niit/