All of the listed income items - passive income, interest income, dividends, and short-term capital gains - from an S corporation are considered investment income for purposes of the Net Investment Income tax. The Net Investment Income tax imposed by section 1411 of the Internal Revenue Code includes interest, dividends, capital gains, rental and royalty income, non-qualified annuities, and income from businesses involved in trading financial instruments or commodities, as well as passive business activities.