Alternative Minimum Tax (AMT) Explained: When Six-Figure Earners Face Unexpected Tax Bills

Most six-figure earners assume their tax return follows a predictable path: income minus deductions equals taxable income, and the bill is roughly what it was last year. The Alternative Minimum Tax (AMT) breaks that assumption. It is a parallel tax system that can override your regular calculation and produce a bill you did not see coming—often in the same year you exercised stock options, received a large bonus, or sold appreciated assets.

This article explains exactly how AMT works, who faces real risk in 2026, which financial events trigger it, and what concrete steps you can take before year-end to limit the damage. This is not personalized tax advice; consult a CPA or tax professional for guidance specific to your situation.

What Is the Alternative Minimum Tax (AMT)?

The AMT is a second, parallel method for calculating federal income tax. If your AMT liability exceeds your regular tax liability, you pay the higher amount. Think of it as a tax floor—a minimum level of tax that deductions and credits cannot push you below, regardless of how many legitimate breaks you qualify for under regular rules.

Congress created the AMT’s predecessor in 1969 after the Treasury Department disclosed that 155 taxpayers with adjusted gross incomes above $200,000 (roughly $1.4 million in today’s dollars) had paid zero federal income tax for the 1966 tax year. Rather than close specific loopholes, Congress built a separate calculation that stripped out preferential tax treatment across the board. Today, the AMT has largely migrated away from its original wealthy targets and increasingly affects upper-middle-income earners instead.

Under AMT rules, you start with regular taxable income, then add back items that received favorable treatment under regular rules—state and local tax (SALT) deductions, certain depreciation methods, and the spread on incentive stock option (ISO) exercises, among others. The result is Alternative Minimum Taxable Income (AMTI), which is typically higher than regular taxable income. You then subtract an exemption, apply AMT-specific rates of 26% or 28%, and compare the result to your regular tax. You pay whichever number is larger.

Who Faces AMT Risk in 2026?

Prior to the 2017 Tax Cuts and Jobs Act (TCJA), roughly 3.1% of all taxpayers were affected by the AMT. Among earners above $200,000, that figure ranged from 18.4% to 69.5%, according to IRS data cited by Charles Schwab. The TCJA raised exemption amounts and phaseout thresholds substantially through 2025, narrowing AMT exposure considerably for most earners in recent years.

2026 is a turning point. The One Big Beautiful Bill Act (OBBBA) made the elevated TCJA exemption amounts permanent and indexed them for inflation—good news on the surface. But the legislation also reset the exemption phaseout thresholds to levels lower than those under the TCJA, and the phaseout itself accelerates faster starting in 2026. The practical result: six-figure earners who comfortably escaped AMT in recent years may find themselves back in range.

As a rough guide, incomes below approximately $88,100 for single filers in 2025 rarely trigger AMT. Above that level, the exemption begins phasing out, which reduces your available offset against AMTI and can sharply increase AMT exposure. Married couples carry additional risk: AMT does not provide the same dependent exemptions or full standard deduction that regular tax rules allow, creating what the IRS Taxpayer Advocate has called a marriage and family penalty embedded in the AMT structure.

If your income exceeds $200,000 and you have any of the income events described below, treat AMT as a real possibility—not a remote one—until you run the actual numbers.

The 3 Biggest Unexpected AMT Triggers

1. Exercising Incentive Stock Options (ISOs)

ISOs receive favorable treatment under regular tax rules: exercising them does not create ordinary taxable income at the time of exercise. Under AMT, however, the “bargain element”—the difference between the stock’s fair market value at exercise and the price you paid—counts as AMT income. You owe AMT on that spread even if you never sell the shares and never receive any cash.

Example: You exercise ISOs at $10 per share when the stock trades at $60. The $50 bargain element is invisible under regular tax but fully included in AMTI. On 10,000 shares, that’s $500,000 added to your AMTI. At the 28% AMT rate, the potential tax exposure on that spread alone exceeds $100,000—without a single share being sold.

2. Sudden Income Spikes

A one-time income surge—a large bonus, RSU vest, deferred compensation payout, or business income distribution—can push you into AMT territory in two compounding ways. First, higher income means a higher AMTI baseline. Second, the AMT exemption phases out as income rises, shrinking the dollar-for-dollar protection that makes the system manageable at moderate income levels.

In 2025, the phaseout rate is $0.25 (25 cents) for every dollar above the applicable threshold. Starting in 2026 under the OBBBA, that phaseout accelerates to $0.50 (50 cents) per dollar—meaning the exemption disappears twice as fast at higher incomes. A taxpayer at $300,000 who retained much of the exemption under 2025 rules could face a substantially reduced exemption in 2026 under the same income level, leaving a larger AMTI exposed to the 26%–28% AMT rate.

3. Large Capital Gains

Selling appreciated investments, real estate, or a business stake generates capital gains that increase AMTI. On their own, capital gains may not trigger AMT. But they frequently stack with other events—an ISO exercise, a bonus, or SALT add-backs—creating a combined AMTI that crosses the tipping point. The year you sell a concentrated stock position or close a significant real estate transaction is exactly the year to run AMT projections proactively, not after the fact.

A Note on SALT Add-Backs

State and local tax deductions—including property taxes—are disallowed entirely under AMT. Any state income tax refund you deducted on a prior federal return must also be added back into AMTI. This add-back is automatic and often surprises taxpayers in high-tax states such as California, New York, and New Jersey, where SALT deductions under regular tax rules can be substantial.

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How AMT Is Calculated: The Basic Steps

The IRS requires Form 6251 (Alternative Minimum Tax—Individuals) to determine whether you owe AMT. Here is the simplified calculation flow:

1. Start with regular taxable income. Use the figure from your Form 1040 after applicable deductions but before any AMT adjustments.
2. Add back AMT preference items and adjustments. These include SALT deductions, the ISO bargain element, accelerated depreciation adjustments, certain passive activity losses, and other itemized deductions that are disallowed under AMT rules.
3. Calculate AMTI. The sum of regular taxable income plus all add-backs equals your Alternative Minimum Taxable Income—the figure the AMT system actually taxes.
4. Subtract the AMT exemption. For 2025, the exemption is approximately $88,100 for single filers and $137,000 for married filing jointly. These amounts are indexed for inflation annually. For 2025, the exemption phases out at $0.25 (25 cents) for every dollar of income above the applicable threshold. Starting in 2026, the OBBBA accelerates that phaseout rate to $0.50 (50 cents) per dollar—so the exemption shrinks twice as fast at higher income levels.
5. Apply AMT tax rates. The first bracket is taxed at 26%; income above a specified threshold is taxed at 28%. For the 2025 tax year, the 28% rate applies to AMTI exceeding $239,100 for single, head of household, and married filing jointly filers.
6. Compare to regular tax and pay the higher amount. If your tentative minimum tax exceeds your regular income tax, the difference is your AMT liability. Report it on Schedule 2 of Form 1040.

The 2026 AMT Shift: Why It’s Back on High Earners’ Radar

The OBBBA made the elevated TCJA exemption amounts permanent and indexed them for inflation going forward—a meaningful protection against the return of pre-2018 AMT exposure. But the same legislation reset the exemption phaseout thresholds lower than under the TCJA and doubled the phaseout rate to $0.50 per dollar starting in 2026. Those two changes together expand the range of incomes meaningfully affected by AMT.

What this means in practice:

• Earners who retained most of their exemption under 2018–2025 rules may see it erode significantly faster in 2026 at the same income level due to the doubled phaseout rate.
• A taxpayer at $300,000 of income who faced minimal AMT exposure in 2024 could face meaningfully higher AMT liability in 2026—without any change in income, deductions, or investment behavior.
• Prior-year AMT calculations are not reliable predictors of 2026 liability. The phaseout thresholds and phaseout rate both changed; your prior-year return is not a useful template.
• Six-figure earners who escaped AMT in 2023 or 2024 should not assume that pattern holds in 2026 and beyond.

The core takeaway: if you have not re-run your 2026 tax projection using the OBBBA rules, do it now—before transactions close, not after.

The AMT Credit: Will You Actually Get That Money Back?

When AMT is triggered by a timing difference—income recognized earlier under AMT than under regular tax, such as an ISO exercise—you may generate an AMT credit. That credit carries forward and can reduce regular tax in future years, but only when your regular tax liability exceeds your AMT liability in those future years.

AMT credits are real and can be valuable. Treating them as guaranteed recovery is a mistake. Consider the scenarios where credits go unused or disappear entirely:

• Income stays consistently high. If your income keeps you in AMT territory year after year, regular tax rarely exceeds AMT, and credits accumulate without becoming usable.
• AMT stems from permanent preference items. SALT disallowance and certain other preference items do not reverse over time. Credits generated from these permanent items may never be recoverable.
• ISO shares decline before sale. You paid AMT on the bargain element at exercise. If the shares drop in value before you sell, you’ve paid tax on income that was never economically realized. The AMT credit does not compensate for that outcome.
• Credits accumulate late in a career. If you’re within ten to fifteen years of retirement and AMT credits are building up, you may not have enough high-regular-tax years remaining to use them efficiently.

Treat AMT credits as a potential future benefit—not a dollar-for-dollar offset to current AMT pain. Well-executed planning minimizes unnecessary AMT first and treats the credit as a secondary consideration.

4 Practical Moves to Reduce Your AMT Exposure

1. Run Multi-Year Projections Before Year-End

The single most effective step is modeling your 2026 and 2027 AMT exposure before transactions are executed. A CPA or tax planning software can identify which income events are most likely to trigger AMT, what your effective AMT rate would be at different income levels, and which years are better suited for large transactions. This analysis is especially important if you hold ISOs, have large unrealized gains, or anticipate a significant income event in either year.

2. Spread Large Transactions Across Tax Years

AMT is frequently a problem of income stacking—multiple large items landing in the same tax year. Strategies to consider:

• Defer a bonus into a lower-income year where the exemption is less likely to phase out fully.
• Stagger ISO exercises across multiple years rather than exercising a large block at once.
• Delay or accelerate a capital gain sale depending on which year poses more AMT risk based on your projections.

Spreading income does not eliminate AMT risk, but it prevents the phaseout from compounding in a single year—particularly important in 2026, when the phaseout rate doubles to $0.50 per dollar.

3. Plan ISO Exercise and Sale Timing Together

If you hold ISOs, the decision to exercise should be coordinated with a plan for the resulting tax liability, including the AMT impact. A same-year sale (disqualifying disposition) avoids AMT on the bargain element but triggers ordinary income tax rates. Holding shares for favorable long-term capital gains treatment preserves tax advantages but creates AMT exposure at exercise. The right answer depends on your income level, the stock’s expected trajectory, and your available cash to cover taxes without selling shares under duress. Model both scenarios with your CPA before acting—there is no universal right answer.

4. Know Your Exact Exemption and Phaseout Range

The difference between owing $0 in AMT and owing several thousand dollars can hinge on a relatively small income shift. If your AMTI is near the phaseout threshold, a $10,000 income decision—taking a consulting project, accelerating a bonus, or selling a stock position—can reduce your exemption by $2,500 under 2025 rules, or by $5,000 under 2026 rules, and produce an AMT bill you did not anticipate. Knowing your specific numbers turns income decisions into tax decisions as well.

What to Do Next: Your AMT Readiness Checklist

If Your Income Is Above $200,000

• Request Form 6251 modeling from your CPA before the end of the tax year. Discovering AMT exposure in April—after transactions are already closed—eliminates all planning options.
• Confirm whether the OBBBA phaseout thresholds affect your 2026 exemption compared to 2025. Ask your preparer to run both years side by side so you can see the difference directly.
• Identify any anticipated income events (bonus, RSU vest, asset sale) and assess their AMT impact before they occur, not after.

If You Hold ISOs or Expect a Large Bonus

• Calculate the AMT impact of any ISO exercise before executing it. The bargain element is taxable under AMT even without a sale—confirm you have liquid assets to cover potential tax before committing to an exercise.
• For bonuses or deferred compensation, evaluate whether timing the receipt in a different tax year meaningfully reduces your AMTI below the phaseout zone.
• In 2026, factor in the accelerated $0.50 phaseout rate when modeling how much of the exemption you will retain at your expected income level.

For All Six-Figure Earners: Lock In Your 2026 Plan by October

• Use IRS Form 6251 instructions or tax software to run a preliminary AMT estimate before involving a professional. It is a rough but useful starting point.
• If you generated AMT credits in prior years, confirm the credit balance and assess whether your current-year income structure is likely to allow any recovery.
• Finalize your transaction timing, exemption strategy, and credit tracking well before December. Year-end planning rushed in the final two weeks is consistently less effective and more likely to miss interactions between income items.

Bottom Line

The AMT is not a penalty for high income alone—it is a penalty for specific combinations of income, deductions, and financial events that push regular tax below a calculated floor. In 2026, the combination of lower phaseout thresholds and a doubled phaseout rate under the OBBBA makes AMT exposure broader than it was for many six-figure earners in 2023 or 2024. The best defense is accurate projection before transactions close, strategic timing of income events, and professional guidance when ISOs, large capital gains, or complex income sources are involved. Prior-year returns are not a reliable guide—re-run the numbers under current law.

This article is for informational purposes only and does not constitute personalized tax, legal, or financial advice. Consult a qualified CPA or tax advisor for guidance specific to your situation. AMT rules are subject to legislative and regulatory change; verify current exemption amounts, phaseout thresholds, and phaseout rates with the IRS or a qualified tax professional before making financial decisions.