The FEIE Stacking Rule: Why Your Excluded Income Still Affects Your Tax Rate

The Foreign Earned Income Exclusion is one of the most powerful tax-saving tools available to U.S. expats. If you qualify, you can exclude up to $130,000 of foreign earned income from U.S. taxation in 2025. That could be $20,000 in tax savings for someone taking the full exclusion.

But there's a critical nuance that catches many expats off guard when they try to estimate their taxes or plan for capital gains: the stacking rule. This rule determines how your excluded income affects the tax rate applied to your other income, even though that excluded income doesn't show up as taxable on your return.

How the Stacking Rule Works

The Foreign Earned Income Exclusion removes income from taxation when calculating how much you owe. That part is straightforward. But when determining what tax bracket applies to your remaining income, the IRS requires you to add that excluded income back into the calculation.

Think of it this way: you get the benefit for excluding the income when figuring out what's taxable, but you don't get an additional benefit for it when figuring out what rate applies. The excluded income "stacks" on top of your other income in determining your marginal income tax rate..

This affects two major areas:

• Your ordinary income tax brackets - determining the rate on wages, self-employment income, and other earned income that exceeds the exclusion amount
• Your long-term capital gains rates - determining whether you qualify for the 0%, 15%, or 20% capital gains brackets

The Capital Gains Surprise

Long-term capital gains receive preferential tax treatment compared to ordinary income. Instead of the standard marginal rates, capital gains are taxed at 0%, 15%, or 20% depending on your total taxable income.

For married couples filing jointly in 2025, the 0% capital gains bracket covers income up to roughly $90,000. Many expats assume that if their wage income is fully excluded through the FEIE, only their capital gain counts toward that $90,000 threshold.

That assumption is wrong.

A Real Client Scenario

Here's a scenario from a recent client consultation:

• Wage income: $130,000 (fully excluded through FEIE)
• Long-term capital gain: $90,000 from investment sale
• Client's expectation: 0% tax rate on the capital gain since taxable income appears to be only $90,000
• Actual result: 15% tax rate applies because total income ($130,000 + $90,000 = $220,000) determines the bracket

On the surface, their math made sense. With wages fully excluded, their taxable income would appear to be just the $90,000 capital gain—right at the edge of the 0% bracket. Zero tax owed.

But that's not how the tax calculation works. The stacking rule requires adding back the $130,000 of excluded wage income when determining which capital gains bracket applies. That puts their total income at $220,000, well into the 15% capital gains bracket.

Instead of zero tax on the gain, they faced roughly $13,500 in capital gains tax.

The tax return will show their wage income as excluded. The return will show only the capital gain as taxable income. But the rate applied to that gain reflects the total income picture, not just what appears on the return.

Net Investment Income Tax Threshold

The stacking rule creates similar issues with the 3.8% Net Investment Income Tax (NIIT). This tax applies to investment income when your modified adjusted gross income exceeds certain thresholds:

• Married filing jointly: $250,000
• Single filers: $125,000
• Married filing separately: $125,000

If you have investment income and your earned income is excluded through the FEIE, you might assume you're nowhere near those thresholds. But the excluded income gets added back when determining whether you've crossed into NIIT territory.

Using the same example: $130,000 excluded wage income plus $90,000 capital gain equals $220,000 total income for NIIT purposes, even though only $90,000 appears as taxable. That puts the couple over the $250,000 threshold, potentially triggering the 3.8% tax on their investment income.

Planning Around the Stacking Rule

Understanding the stacking rule matters most when you're estimating taxes for the current year or making decisions about when to realize capital gains.

If you're taking the Foreign Earned Income Exclusion and have investment income or capital gains, don't calculate your tax liability based solely on what shows as taxable income. Factor in the excluded amount to determine your actual tax brackets.

This becomes especially important for timing decisions. Spreading capital gains across multiple years might make sense even when your current-year taxable income appears low. The stacking rule can push you into higher brackets faster than you expect.

For estimated tax payments, the stacking rule means you might owe more than a quick calculation suggests. Running the numbers correctly prevents underpayment penalties and surprises when you file.

The Bottom Line

The Foreign Earned Income Exclusion remains one of the best tax benefits available to U.S. expats. It delivers real, substantial tax savings. But it's not a complete exemption from the tax system.

The stacking rule ensures that excluded income still influences your overall tax picture. It affects your bracket for ordinary income, your rate for capital gains, and your threshold for the Net Investment Income Tax. Your excluded income doesn't disappear from the calculation - it just shifts to a different part of the formula.

When you're estimating your tax liability or planning for capital transactions, remember: what you see on the tax return isn't the full story of how your tax gets calculated. The excluded income is still working in the background, determining which rates apply to everything else.