AMT Basics: The Parallel Tax System
AMT operates as a parallel tax system. You calculate your tax both ways (regular and AMT) and pay the higher amount. AMT has its own rules, exemptions, brackets, and adjustments distinct from the regular tax system.
AMT calculation: start with taxable income, add back certain 'preferences' and 'adjustments' to get Alternative Minimum Taxable Income (AMTI). Subtract the AMT exemption. Apply AMT rates: 26% on first $239,100 of AMTI (2026) and 28% on the excess.
Compare AMT to regular tax: if AMT is higher, you owe the difference as 'tentative minimum tax' on top of your regular tax. If regular tax is higher, no AMT owed.
2026 AMT exemption: $88,100 single / $137,000 married filing jointly. Phase-outs begin at $626,350 / $1,252,700 of AMTI, reducing the exemption by 25 cents per dollar of AMTI above the threshold. The exemption is completely phased out at AMTI of $978,750 / $1,800,700.
Strategic implication: AMT primarily hits taxpayers who have substantial AMT preferences/adjustments AND aren't in the highest regular brackets. High-bracket taxpayers (top 35-37%) often aren't affected by AMT because regular tax exceeds AMT regardless of preferences.
Major AMT Preferences and Adjustments
ISO bargain element: when you exercise Incentive Stock Options without same-year sale, the spread between FMV and strike price is added to AMTI. This is the most common AMT trigger for tech executives.
State and local tax deduction: SALT is deducted for regular tax but ADDED BACK for AMT. So your $10K SALT deduction (capped) reduces regular tax but doesn't reduce AMT. For high-SALT taxpayers, this can push AMT above regular tax.
Private activity municipal bond interest: certain types of muni bonds (PABs) generate tax-exempt interest for regular tax but taxable for AMT. Most general-obligation munis are not PABs; check before purchasing if AMT is a concern.
Depreciation differences: real estate and equipment may have different depreciation schedules for regular tax vs AMT, creating preference items.
Net operating loss (NOL) deduction: regular NOLs differ from AMT NOLs (limited to 90% of AMTI for AMT purposes pre-TCJA; rules have evolved).
Refundable credits: some refundable credits applied for regular tax aren't allowed for AMT calculation purposes.
ISO Exercises and AMT Strategy
The classic AMT trap: exercise large ISO grants near year-end, hold for qualifying disposition (more than one year from exercise AND more than two years from grant). The bargain element is an AMT preference item that creates significant AMT in the year of exercise — even though you have no regular taxable income from the exercise.
Concrete example: 10,000 ISOs with $10 strike, current FMV $80. Exercise but don't sell. Bargain element: $700,000. AMTI increases by $700K. With $200K of other taxable income, AMTI is $900K. AMT exemption fully phased out. AMT tax: 28% × $900K minus 0 exemption ≈ $252K. Regular tax on $200K: ~$37K. AMT owed: $215K — payable in cash with no liquidity event.
Strategic mitigations:
Exercise in batches: spread large exercises across multiple years, keeping each year's AMTI below the phase-out threshold and minimizing AMT exposure each year.
Same-year exercise and sale (disqualifying disposition): converts the spread to ordinary income for regular tax purposes (no AMT preference). Sacrifices LTCG treatment but avoids AMT entirely. Often the right answer when AMT exposure is large.
Exercise early in the year: if the stock crashes between exercise and tax filing, you can sell to crystallize a tax loss (regular short-term capital loss) to offset some of the AMT impact. Year-end exercise leaves no time for this.
AMT credit: the AMT paid creates a credit that can offset future regular tax to the extent regular tax exceeds AMT in those years. Eventually you 'get back' the AMT paid — but the timing can be many years.
SALT Cap Interaction with AMT
Pre-TCJA, the SALT add-back for AMT was a major AMT trigger for high-SALT-state residents. Post-TCJA with the $10K SALT cap for regular tax, the AMT add-back is less impactful — but still relevant for certain situations.
For someone with $30K of SALT (state income tax + property tax): regular tax allows $10K (capped). AMT adds back the full $10K (no cap distinction). So AMTI is $10K higher than regular taxable income from this item.
For someone whose state tax exceeds $50K (high earners in high-tax states), the regular tax SALT deduction is still $10K (capped). AMT add-back is the same $10K. The cap effectively limits how much the SALT-AMT-trap matters.
Strategic note: states' Pass-Through Entity Tax (PTE) elections that bypass the SALT cap by paying state tax at entity level — these payments are deducted by the entity for federal regular tax purposes (above-the-line). For AMT, PTE-paid state taxes ARE NOT a SALT add-back — they were never deducted as SALT in the first place. So PTE elections are AMT-friendly for high-SALT business owners.
Private Activity Municipal Bonds
Most municipal bonds generate interest that's exempt from both federal regular tax AND federal AMT. But Private Activity Bonds (PABs) — munis issued for non-government purposes like airport authorities, hospitals, university construction — generate interest exempt from regular tax but TAXABLE for AMT.
If AMT is a concern, avoid PABs. Check before purchasing — major bond databases identify PAB status. Building general-obligation muni positions and avoiding PABs eliminates this AMT preference.
Mutual fund/ETF muni funds vary in PAB exposure. Vanguard's basic intermediate-term tax-exempt fund (VWITX) holds some PABs. Specialized 'AMT-free' muni funds explicitly exclude PABs (e.g., VWAHX). For AMT-exposed investors, the AMT-free version is worth slightly lower yields.
Geographic muni concentration: in-state munis often have PAB components for state authorities. Out-of-state diversified muni holdings may have less PAB exposure. Evaluate before buying.
After-tax yield calculation: PAB interest is fully tax-free for non-AMT taxpayers. For AMT-exposed taxpayers, the after-AMT yield is much lower. Make sure you're comparing apples to apples in your bond allocation decisions.
Year-End AMT Planning
December 31 is the deadline for most AMT planning moves. Common year-end actions:
Calculate projected AMT before year-end. Use Form 6251 calculator or AMT calculator to estimate exposure. If AMT is likely, time discretionary moves accordingly.
Defer large deductions to next year if AMT-affected. Charitable contributions, deferred SALT payments, etc. can be timed to fall in non-AMT years where they provide more benefit.
Accelerate income that's only taxable for regular tax (not AMT). State income tax refunds (from prior year) are taxable for regular tax in the year received but not for AMT. Receiving them in an AMT year minimizes their tax cost.
ISO exercise timing: don't exercise late in the year if you might want to sell quickly to avoid AMT. Better to exercise early in the year when you have time to evaluate and respond.
Roth conversion implications: Roth conversions are ordinary income for both regular tax AND AMT. They don't trigger AMT (no preference item involved). But they push up overall income, potentially affecting AMT exemption phase-outs.