Glossary term
Net Investment Income (NII)
Net investment income is investment income reduced by certain allocable expenses and is used in the net investment income tax framework.
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What Is Net Investment Income?
Net investment income, or NII, is investment income reduced by certain allocable expenses. In U.S. tax planning, the term is especially important because it is used in the net investment income tax, a surtax that may apply to higher-income taxpayers.
NII can include interest, dividends, capital gains, rental and royalty income, nonqualified annuity income, and certain income from passive activities. It does not include every kind of income, and the tax rules contain exclusions, expense rules, and thresholds that determine the final result.
Key Takeaways
- Net investment income starts with investment income and subtracts certain related expenses.
- It is central to the net investment income tax calculation.
- Common components can include interest, dividends, capital gains, rentals, royalties, and passive activity income.
- Wages, Social Security benefits, tax-exempt interest, and many retirement-plan distributions are generally outside the NII bucket.
What Can Count as NII
The tax definition is more specific than the everyday phrase investment income. A taxpayer may have investment-related cash flow that does not count, or income that counts only after activity classification and expense allocation are considered.
Income Type | Typical NII Treatment |
|---|---|
Interest and dividends | Often included, unless specifically excluded. |
Capital gains | Often included when gains are from investments. |
Rental and royalty income | May be included, depending on activity and exceptions. |
Wages and self-employment income | Generally not net investment income. |
Connection to the NIIT
The net investment income tax, or NIIT, applies only when the taxpayer has both net investment income and modified adjusted gross income above the applicable threshold. The tax is generally calculated on the lesser of net investment income or the excess of modified adjusted gross income over the threshold.
That structure means NII alone is not enough to know whether the surtax applies. A taxpayer also needs filing status, modified adjusted gross income, and the details of what income and expenses are included.
Tax Planning Context
NII can affect decisions about realizing capital gains, timing income, harvesting losses, structuring rental activity, and using tax-advantaged accounts. It can also make the character of income matter. Interest, dividends, rental income, and capital gains may be treated differently from wages or qualified retirement-plan distributions.
Expense allocation can matter as well. Investment interest, advisory fees, state taxes, and other deductions may affect the net amount only when the rules allow them to be connected to the investment income.
Because the definition is tax-specific, the same investment portfolio can produce different planning concerns depending on filing status, income level, realization of gains, and whether activities are passive or active.
The Bottom Line
Net investment income is a tax-specific measure of investment income after certain expenses. It matters because it helps determine exposure to the net investment income tax, especially for higher-income households with taxable investment income.