Incentive Stock Options and the AMT Trap

Published September 24, 2026 · By Shane Weng, BookBright Solutions LLC

RSUs surprise people with a withholding gap. Incentive Stock Options surprise people in a different, more dangerous way: it is possible to owe tens of thousands of dollars in tax on stock you still hold and have not sold a single share of. That is the Alternative Minimum Tax, and for tech employees at pre-IPO or recently-public companies, it is one of the most expensive mistakes we see.

ISOs are taxed differently than RSUs

We covered how RSUs are taxed in an earlier article — ordinary income at vesting, capital gain or loss at sale. ISOs don't work that way. Under the regular tax system, exercising an ISO and holding the shares generally creates no regular taxable income at all at the time of exercise. That is the whole appeal of ISOs over Non-Qualified Stock Options (NSOs): no ordinary income hit just for exercising.

The catch is that the regular tax system is not the only system that runs your return.

The AMT trap

The Alternative Minimum Tax is a parallel tax calculation that adds back certain items the regular system lets you exclude — and the spread between your ISO strike price and the stock's fair market value at exercise is one of them. Your return is effectively computed twice, once under regular rules and once under AMT rules, and you pay whichever number is higher.

This means it is entirely possible to exercise a large ISO grant, owe nothing under the regular calculation, and still generate a five- or six-figure AMT bill — for stock you are still holding, with zero cash in hand from a sale to pay that bill with. For employees at private companies where the shares can't be sold on the open market, this is the scenario that causes real financial strain.

Why this hits Bay Area tech employees especially

A few things stack together in this market that make the AMT trap more common here than almost anywhere else:

• 409A valuations move fast. A company that raises a round, has a strong quarter, or approaches an IPO can see its 409A valuation jump well ahead of a public listing — widening the exercise spread on options granted years earlier at a much lower strike price.
• Early exercise and post-termination exercise windows push people to make an exercise decision on a deadline, sometimes without time to model the AMT consequence first.
• Multiple grants, multiple strike prices, multiple vintages. Employees who have been at a company for years are often sitting on option pools issued at very different strike prices, which makes "how much can I exercise before AMT bites" a genuinely complex calculation, not a rule of thumb.

Qualifying vs. disqualifying dispositions

The other piece of the ISO puzzle is what happens when you eventually sell. Meet specific holding-period requirements from both the grant date and the exercise date, and the entire gain can be taxed at long-term capital gains rates — a real advantage over RSUs and NSOs. Sell too soon, and it becomes a "disqualifying disposition," part of the gain gets recharacterized as ordinary income, and the AMT picture from the exercise year has to be reconciled against what actually happened at sale.

Get the timing right and ISOs can be the most tax-efficient form of equity compensation available. Get it wrong — or exercise without a plan for the AMT bill it creates — and the same grant becomes a cash-flow problem in the exercise year and a messy amended-return situation later.

Where we see people get burned

• Exercising a large block of options in December without modeling the AMT impact first.
• Not knowing that AMT paid in one year can generate a credit usable in future years — and never tracking or claiming it.
• Filing an 83(b) election (or missing the window to file one) on early-exercised shares without understanding what it locks in.
• Treating "the company's exercise portal shows I can afford this" as the same question as "will this trigger AMT."

What actually helps

The right move depends entirely on your specific grant details — strike price, current 409A or market value, how many shares you're sitting on, your other income for the year, and how close the company is to a liquidity event. There is real planning available here: spreading exercises across tax years, timing around the AMT exemption phaseout, coordinating with other income events, and tracking the AMT credit forward so you actually use it. None of it is one-size-fits-all, and running the wrong exercise strategy on your own is exactly how a good equity grant turns into a bad tax year.

Bottom line

If you're holding unexercised ISOs — especially at a private company, or one that has recently seen its valuation move — the question is not just "should I exercise," it's "what does exercising do to this year's tax return before I sell anything." That question deserves a real model of your numbers, not a guess.