The 3.8% Net Investment Income Tax That Hits High-Earning Retirees

What the Net Investment Income Tax Actually Is

The Net Investment Income Tax, commonly called the NIIT, was enacted as part of the Affordable Care Act in 2013. It imposes a 3.8% surtax on the lesser of net investment income or the amount by which modified adjusted gross income exceeds a threshold. The NIIT thresholds are: $200,000 for single filers and heads of household, $250,000 for married filing jointly, and $125,000 for married filing separately. These thresholds have never been adjusted for inflation since the tax was enacted. Net investment income for NIIT purposes includes interest income, dividend income, capital gains from selling investments, rental income from passive investments, royalty income, and income from passive business activities. It does not include wages, self-employment income, distributions from traditional IRAs or 401(k)s (those are ordinary income, not investment income), Social Security benefits, or income from active business participation. The math works like this. A single retiree has $180,000 in MAGI from Social Security, RMDs, and a pension - below the $200,000 threshold. They also receive $30,000 in dividends and capital gains from a brokerage account. Their total MAGI is $210,000. They exceed the $200,000 threshold by $10,000. The NIIT applies to the lesser of their net investment income ($30,000) or the excess MAGI ($10,000). They owe 3.8% on $10,000 - a $380 NIIT bill. Now consider a retiree with $220,000 in MAGI and $40,000 in net investment income. They exceed the threshold by $20,000. The NIIT applies to the lesser of $40,000 or $20,000 - so they owe 3.8% on $20,000 = $760. If their MAGI were $260,000 (exceeding the threshold by $60,000), the NIIT would apply to the full $40,000 in investment income - $1,520.

How RMDs Can Trigger NIIT on Investment Income

One of the most common ways retirees unexpectedly get hit by the NIIT is through the interaction between Required Minimum Distributions and investment income thresholds. RMDs from traditional IRAs and 401(k)s are ordinary income, not investment income. They are not themselves subject to the NIIT. However, they count toward MAGI - and a large RMD can push total MAGI above the NIIT threshold, causing previously non-NIIT investment income to become subject to the 3.8% surtax. Consider a married retiree couple with the following 2026 income: $40,000 in Social Security (of which 85% is taxable = $34,000 in AGI), $60,000 in RMDs from traditional IRAs, and $30,000 in qualified dividends and long-term capital gains from a taxable brokerage account. Their MAGI: approximately $124,000 from SS and RMDs plus $30,000 investment income = $154,000. Well below the $250,000 married threshold. No NIIT. Now suppose their IRA balance has grown over the years and their RMDs have increased to $120,000. MAGI: $34,000 in taxable SS + $120,000 RMDs + $30,000 investment income = $184,000. Still below the threshold. Still no NIIT. But add a Roth conversion of $80,000 in the same year: MAGI becomes $264,000 - $14,000 above the $250,000 married threshold. Now the NIIT applies to the lesser of $30,000 investment income or the $14,000 excess MAGI = $532 in NIIT. The Roth conversion did not generate investment income, but it pushed the couple over the threshold and activated NIIT on their existing dividend income. This interaction makes income planning for retirees with investment accounts more complex than many expect. Roth conversions, voluntary IRA distributions, and even pension lump-sum elections all count toward MAGI and can affect NIIT exposure.

The Combined Capital Gains Rate for Higher-Income Retirees

The NIIT changes the effective tax rate on investment income significantly for those above the threshold. Most people talk about capital gains taxes as if the rates are simply 0%, 15%, or 20%. For higher-income retirees, the true combined rate is higher. At the 20% long-term capital gains rate (which applies when taxable income exceeds $583,750 for married couples in 2026), the NIIT adds 3.8% - bringing the combined federal rate to 23.8%. In a state with a 6% income tax on capital gains, the total state and federal combined rate approaches 30% on long-term gains. Even at the 15% long-term capital gains rate tier, the NIIT adds 3.8% for those above the MAGI threshold, making the combined federal rate 18.8% - materially higher than the headline 15%. For retirees managing taxable investment accounts alongside RMDs and Social Security, the question of when to harvest gains - and how much to harvest in any given year - requires modeling the full combined rate including NIIT exposure, not just the nominal capital gains rate. Income sources that do not count toward MAGI for NIIT purposes include Roth IRA withdrawals and loans from properly structured life insurance policies. Managing which income sources fund living expenses can help control MAGI and reduce NIIT exposure in years when investment income is elevated.