Incentive Stock Options and the AMT: Planning Your Exercise Windows

ISOs can offer favorable tax treatment, but the alternative minimum tax turns an ordinary exercise decision into a multi-year planning exercise.

Incentive stock options (ISOs) remain common at Bay Area startups and growth-stage companies. Unlike RSUs, options give you the right, not the obligation, to buy shares at a fixed strike price. When a company's value has risen well above that strike, the potential economic benefit can be significant. So can the tax complexity, because ISOs interact with the alternative minimum tax (AMT) in ways that surprise even sophisticated employees.

The basic ISO rules

According to IRS Topic 427, you generally do not recognize regular income when you receive or exercise an ISO. To receive long-term capital gains treatment on the full spread, you must hold the shares at least two years from the grant date and one year from the exercise date. If you sell before meeting both tests, the sale is a "disqualifying disposition" and some or all of the gain is taxed as ordinary wage income. Your employer reports each exercise on Form 3921, which contains the dates and values you will need at tax time.

Where the AMT comes in

The AMT is a parallel tax calculation with its own rules. When you exercise ISOs and hold the shares past year-end, the spread between the strike price and fair market value at exercise is an adjustment for AMT purposes, even though it is not regular taxable income. If the AMT calculation produces a higher liability than your regular tax, you pay the difference.

For tax year 2026, the IRS sets the AMT exemption at $90,100 for unmarried filers and $140,200 for married couples filing jointly. The exemption begins to phase out at $500,000 and $1,000,000 of alternative minimum taxable income, respectively. A large exercise can push someone with an otherwise ordinary income profile well into AMT territory.

The AMT you pay on an ISO exercise is not necessarily lost. It may generate a minimum tax credit that can be used in future years when your regular tax exceeds your tentative minimum tax. The mechanics are reported on Form 6251 and related schedules, and the credit can take years to recover in full.

The dual-basis problem

Shares acquired through an ISO exercise carry two different cost bases: the strike price for regular tax purposes and the fair market value at exercise for AMT purposes. When you eventually sell, the regular tax gain and the AMT gain differ, and the difference affects how much of your prior AMT credit you can use. Keeping careful records of each exercise lot is essential.

Planning considerations

Employees with ISOs often weigh several approaches:

• Exercising up to the AMT crossover. Some people exercise only the number of shares that keeps their tentative minimum tax roughly equal to their regular tax for the year, spreading exercises across multiple tax years.

• Exercising early in the year. An exercise in January gives you until December to decide whether to hold the shares or sell them in a disqualifying disposition, which can eliminate the AMT adjustment for that year if the stock has fallen.

• Coordinating with other income. A year with lower salary or a gap between jobs may create room for exercises at a lower overall cost.

• Liquidity for the tax bill. AMT is due even if the shares cannot be sold, which is a real concern for private company employees. The cash to pay it has to come from somewhere.

  
  

California adds another layer

California has its own AMT calculation, and it taxes capital gains as ordinary income at rates that reach 13.3% for very high earners, per NerdWallet's summary of California rates. The federal benefit of long-term capital gains treatment on qualifying ISO sales does not carry over to your state return.

What to remember

ISOs reward patience and planning. The potential to convert a large spread into long-term capital gains is real, but so is the risk of paying AMT on paper gains that later evaporate. The decision to exercise, how many shares, and when, is best made with a full-year tax projection in hand. This article is educational and does not constitute tax advice; please consult a qualified tax professional before exercising options.

Important Disclosures

Important Disclosures: Propulsion Capital Management is an investment adviser registered with the State of California Department of Financial Protection and Innovation. Registration does not imply a certain level of skill or training. This article is provided for general informational and educational purposes only and does not constitute investment, tax, legal, or accounting advice, nor an offer or solicitation to buy or sell any security or to adopt any particular investment strategy. The information is believed to be accurate as of the date of publication but is subject to change without notice; tax laws and regulations change frequently and their application depends on individual facts and circumstances. Nothing herein should be relied upon as a substitute for personalized advice from a qualified professional. Investing involves risk, including the possible loss of principal, and past performance is no guarantee of future results. Diversification does not ensure a profit or protect against loss. Any examples are hypothetical, are for illustrative purposes only, and do not reflect the experience of any client. Links to third-party websites are provided for convenience; Propulsion Capital Management does not endorse, and is not responsible for, the content of third-party sites. Propulsion Capital Management does not provide tax or legal advice; please consult your tax adviser or attorney regarding your specific situation.