ISOs and AMT: The Tax Surprise Most Tech Employees Get

Incentive stock options look like the cleanest equity grant on paper: no tax on the grant, no tax on exercise, long-term capital gains when you sell. That story is mostly true. The part it leaves out is the Alternative Minimum Tax, and it has caught a lot of well-compensated tech employees completely off guard.

What Actually Happens When You Exercise ISOs

When you exercise an ISO, the spread between your strike price and the fair market value of the stock — called the bargain element — does not appear on your W-2. Your employer does not withhold anything. Under regular income tax rules, nothing taxable happened yet.

The AMT sees it differently. The bargain element is an AMT preference item, which means it gets added back into your Alternative Minimum Taxable Income (AMTI). If your AMTI crosses the AMT exemption threshold, you owe a parallel tax calculated at either 26% or 28% on that adjusted income. You write that check in April even if the stock has already dropped and you never sold a share.

For 2025, the AMT exemption is $88,100 for single filers and $137,000 for married filing jointly, phasing out above $626,350 and $1,252,700 respectively. High earners in tech often clear these thresholds on ordinary income alone, which means the full bargain element gets hit at the AMT rate.

The Rules, the Math, and the Watchouts

Here is a concrete version of what this looks like.

Say you have ISOs with a strike price of $1 per share. The company's current 409A valuation is $10 per share. You exercise 20,000 shares. Your out-of-pocket cost is $20,000. The bargain element — the phantom income the AMT cares about — is $180,000.

If you are already phased out of the exemption, you could owe AMT of roughly $46,800 to $50,400 on that $180,000 depending on your full tax picture. You paid $20,000 to acquire shares and now owe taxes that dwarf what you paid. The stock is illiquid. The cash has to come from somewhere else.

Two other watchouts worth naming:

The California problem is real. California does not recognize the ISO exercise exclusion at all. California treats the bargain element as ordinary income at exercise, regardless of federal AMT. If you live in California, your state tax bill arrives alongside the federal AMT bill, and neither cares whether the shares are liquid.

The disqualifying disposition trap. If you exercise and then sell within the same calendar year, or within a year of exercise, you lose ISO status and the sale becomes ordinary income. You might think this helps avoid AMT since the AMT preference disappears. Sometimes it does. Sometimes it just trades a lower AMT bill for a higher ordinary income bill. Run the numbers before you assume a quick sale is the safer path.

A Worked Example: The Multi-Year Exercise Strategy

In my work with tech employees at pre-IPO and recently public companies, the most common mistake I see is treating ISOs as an all-or-nothing decision. Exercise everything at once to start the capital gains clock, or wait until a liquidity event. Both extremes tend to create the largest AMT exposure.

A more controlled approach is to calculate your AMT breakeven each year, which is the maximum bargain element you can trigger without generating incremental AMT above your regular tax liability. Below that number, you owe no AMT. Above it, each dollar costs you roughly 28 cents in AMT.

Imagine the same scenario spread across three years. Instead of exercising all 20,000 shares in year one and absorbing $180,000 of AMTI at once, you exercise a block each year sized to stay at or just below the breakeven. You start the long-term holding clock on each tranche, smooth the tax cost, and avoid the cliff.

This is where the AMT credit becomes relevant. Any AMT you do pay is not lost forever. It becomes a credit (Form 8801) that offsets regular income tax in future years when your regular tax liability exceeds what AMT would have been. The credit can carry forward indefinitely. The recovery timeline depends on your income profile, but for most high earners it plays out over three to seven years.

I had a client (illustrative example) who exercised $400,000 in bargain element the year before an IPO without running the numbers. The AMT bill was over $90,000. The stock dropped 60% post-IPO before he was past his lockup. He recovered most of the AMT credit over the following four years, but the cash flow stress in year one was severe and avoidable.

How This Connects to the Equity Compensation Pillar

ISO planning does not live in isolation. It intersects with how you think about RSUs vesting in the same year, how you manage concentrated stock after a liquidity event, and whether your equity is in a taxable account or a deferred structure. The parent guide, Equity Compensation: A Practical Guide to RSUs, ISOs, and NSOs, covers the full landscape, including how ISOs compare to NSOs and RSUs and when each form of grant is actually preferable.

Within the Sporos framework, ISO exercise planning sits in the Soil layer, the tax architecture stage where decisions made years before retirement determine how much of your wealth survives into the next phase.

Frequently Asked Questions

Does exercising ISOs always trigger AMT?

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

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

Yes, to a degree. The AMT credit is based on the tax you paid, not on the stock value. If the stock drops to zero and you hold a $50,000 AMT credit, that credit is still real. You recover it in years when your regular tax exceeds your tentative minimum tax.

What if I exercise and sell in the same year?

A same-year sale of ISO shares is a disqualifying disposition. The bargain element at exercise becomes ordinary income reported on your W-2. AMT typically does not apply to that portion. Whether this is better or worse than paying AMT and holding depends on the stock price, your bracket, and the state you live in.

Does California have its own AMT?

California does not have a separate AMT system, but it does not allow the federal ISO exclusion. The bargain element is ordinary income for California purposes at exercise, taxed at California's top marginal rate, currently 13.3%.

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 has already appreciated, the larger the bargain element and the more compressed your planning window becomes.

Is the AMT credit refundable?

No, it is a nonrefundable credit. It can only offset regular income tax liability. If your regular tax is zero in a given year, the credit carries forward rather than generating a refund.

What to Do Next

1. Pull your option grant agreement and identify which grants are ISO versus 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 rather than concentrating exercise in a single tax 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 — verify current rules before acting. Consult with qualified professionals for guidance specific to your situation.