ISOs and AMT: The Tax Surprise Most Tech Employees Get

Exercising incentive stock options (ISOs) can trigger the Alternative Minimum Tax (AMT) on income you never received in cash. The spread between your strike price and the stock's fair market value at exercise (the bargain element) is added to your AMT income even though it never touches your W-2, and if it pushes you past your exemption you owe tax at 26% or 28% that April, whether or not you ever sold a share. One approach is to size each year's exercise against your AMT breakeven and use the AMT credit to recover the tax over time.

What Happens When You Exercise

Under the regular income tax, exercising an ISO is a nonevent and nothing is withheld; under the AMT, the bargain element is added back into your Alternative Minimum Taxable Income (AMTI).

For 2026, the AMT exemption is $90,100 for single filers and $140,200 for married filing jointly. It phases out by 50 cents for every dollar of AMT income above $500,000 single and $1,000,000 joint (the July 2025 tax law lowered those starting points and doubled the phaseout rate from 25%). High earners can lose part or all of the exemption, and a large bargain element can then be taxed at the full AMT rate.

Concretely: a $1 strike, a $10 409A valuation, and a 20,000-share exercise costs $20,000 out of pocket but creates a $180,000 bargain element. If you are already phased out of the exemption, that could mean roughly $46,800 to $50,400 of AMT, a bill that dwarfs what you paid for shares you cannot yet sell.

Two Watchouts Worth Naming

California adds its own layer. The state has its own AMT, with a top rate of 7%, and the ISO bargain element counts toward it, so a large exercise can produce a California AMT bill alongside the federal one. California's regular income tax does not tax the exercise itself.

The disqualifying disposition trap. Sell within 2 years of the grant date or within 1 year of exercise and the sale is a disqualifying disposition: the bargain element becomes ordinary income. A disqualifying sale in the same calendar year as the exercise removes the AMT adjustment for those shares, so it can avoid AMT while trading it for a higher ordinary income bill. Run the numbers before assuming a quick sale is safer.

The Multi-Year Exercise Strategy

The most common mistake I see with tech employees is treating ISOs as all-or-nothing: exercise everything at once to start the capital gains clock, or wait for a liquidity event. Both extremes tend to create the largest AMT exposure.

A more controlled approach is to calculate your AMT breakeven each year: the maximum bargain element you can trigger without owing AMT above your regular tax. Below that number, no AMT; above it, each dollar costs roughly 26 to 28 cents, and more inside the exemption phaseout. Spread the same 20,000-share exercise across three years, sized at or below breakeven, and you smooth the tax cost while starting each tranche's long-term holding clock.

AMT you do pay becomes a credit (Form 8801) that offsets regular income tax in years when your regular liability exceeds what AMT would have been, carrying forward indefinitely; recovery typically plays out over three to seven years.

Consider a hypothetical client who exercised $400,000 in bargain element the year before an initial public offering (IPO) without running the numbers. The AMT bill was over $90,000, and the stock dropped 60% post-IPO before his lockup ended. He recovered most of the credit over four years, but the year-one cash flow stress was avoidable.

How This Connects to the Equity Compensation Pillar

ISO planning intersects with restricted stock units (RSUs) vesting in the same year and concentrated stock after a liquidity event. The parent guide, Equity Compensation: A Practical Guide to RSUs, ISOs, and NSOs, covers the rest. This is tax planning work, decided years before the money is needed.

Frequently Asked Questions

Does exercising ISOs always trigger AMT?

Not always. If the bargain element is small enough that your AMTI stays below your exemption, no AMT is due; the trigger depends on your total income, deductions, and filing status.

Can I get the AMT credit back if the stock drops?

Yes. The credit is based on the tax you paid, whatever the stock does afterward, so even if the stock goes to zero you can recover it in years when your regular tax exceeds your tentative minimum tax.

Does California have its own AMT?

Yes. California has its own AMT, with a top rate of 7%, and the ISO bargain element is an adjustment for it, the same way it is federally. California's regular income tax does not tax the exercise. When you later sell, the gain is taxed at California's ordinary rates, up to 13.3%, since the state has no lower capital gains rate.

When should I start thinking about ISO exercise timing?

Ideally one to two years before a potential liquidity event, while shares are still at a lower 409A valuation. The more the stock appreciates, the larger the bargain element and the tighter your planning window.

What to Do Next

1. Pull your option grant agreement and identify which grants are ISO versus nonqualified stock option (NSO). Many employees have both without realizing it.
2. Run a pro forma AMT calculation with your tax advisor before exercising anything, using current 409A valuations and your expected income for the year.
3. Map out a multi-year exercise schedule that targets the breakeven zone each year.
4. If you have already paid AMT in a prior year, locate your Form 8801 and confirm your credit carryforward is being tracked and applied.

The information provided is for educational purposes only and does not constitute investment, legal, or tax advice. Tax law changes frequently, so verify current rules before acting. Consult with qualified professionals for guidance specific to your situation.