An example of net investment income and taxes
An individual who generated $10,000 in annual net profits on stocks and $1,000 in dividend income would be taxed at the respective tax rates corresponding to each of those profit sources. If that individual had modified adjusted gross income of $300,000 that year, he or she would also be subject to the net investment income tax.
Because this single filer had MAGI above the $200,000 NII tax requirement threshold, he or she would also be taxed an additional 3.8% on the combined net investment income of $11,000 for that year. He or she would owe an extra $418 in NII taxes.