Exercising an ISO and holding the shares creates no regular income tax, but the spread between your strike price and fair market value at exercise counts as income for the alternative minimum tax. For 2026 the AMT exemption is $90,100 for unmarried filers and $140,200 for joint filers, per the IRS. A large enough spread eats that exemption.
Two things happen at exercise. Only one shows up on your regular return.
The IRS is direct about the first one. "For the regular tax, no income is recognized when an incentive stock option (ISO), as defined in section 422(b), is exercised," says the IRS in the Instructions for Form 6251 (2025), at line 2i. The same paragraph then says that rule does not apply for the AMT.
So the second thing. The excess of the fair market value of the stock over what you paid for it, the bargain element, goes on Form 6251 as an AMT adjustment in the year you exercise. Nothing arrives in your paycheck. No shares are sold. Your W-2 does not change. But a number lands on a parallel tax calculation that most option holders have never run.
Your employer sends a Form 3921 after an ISO exercise, per IRS Topic No. 427 (page last reviewed April 28, 2026). That form carries the grant date, the exercise date, the exercise price, and the fair market value at exercise. It is the input, not the answer.
How the exemption gets consumed
The AMT calculation gives you an exemption, then phases it out as income climbs. For tax year 2026, the IRS put the exemption at $90,100 for unmarried individuals, phasing out from $500,000, and $140,200 for married couples filing jointly, phasing out from $1,000,000 (IRS news release IR-2025-103, October 9, 2025, reflecting Revenue Procedure 2025-32).
Above the exemption, the rate schedule kicks in. For 2025, the Instructions for Form 6251 set the 26% rate on the first $239,100 of taxable excess, with 28% above that. The 2026 versions of those bracket figures are indexed and I have not confirmed them from a primary source, so treat the 2025 numbers as the last confirmed ones.
Keep in mind the ordering. A senior scientist at a Sorrento Valley company earning well into six figures may already be close to the phase-out range before a single option is exercised. The bargain element stacks on top of that, not underneath it.
An illustrative hypothetical, not a client
The following is a hypothetical example for illustration only. It is not a real client, not a composite of real clients, and not a projection of anyone's result.
Assume a strike price of $2.00 on 40,000 vested ISOs at a private San Diego company, and a most recent 409A valuation of $11.00 per share. Exercising all 40,000 costs $80,000 out of pocket and produces a bargain element of $9.00 per share, or $360,000, which is the figure that flows to Form 6251. Regular taxable income does not move by a dollar. Let's hold the 409A constant at $11.00 for this example, because in the real world it moves between the day you decide and the day the paperwork clears, and that alone changes the answer.
What that $360,000 actually produces in AMT depends on filing status, other income, state of residence, and the rest of the Form 6251 calculation. That is the part to run with a CPA before exercising, not after. Also worth asking your CPA about: AMT paid on an ISO exercise may generate a minimum tax credit that can be applied in later years (Form 8801), which changes how you think about the cost, though it does not change when the payment is due.
Three paths, same options
The exercise-and-hold decision is not a settled answer. It is a tradeoff between a tax rate and a risk you are choosing to carry.
| What happens | Exercise and hold past year-end | Exercise and sell same year (disqualifying disposition) | Exercise, hold, sell as qualifying disposition |
|---|---|---|---|
| Regular tax at exercise | None (IRS Topic No. 427) | None at exercise itself | None (IRS Topic No. 427) |
| AMT adjustment at exercise | Yes. Bargain element reported on Form 6251, line 2i (Instructions for Form 6251, 2025) | No adjustment required. If you exercise and dispose of that stock in the same year, regular tax and AMT treatment are the same (Instructions for Form 6251, 2025) | Yes, in the exercise year |
| Holding period required | Clock running, not yet met | Fails it by design | At least 2 years from grant date and 1 year from exercise date (IRS Publication 5992, rev. 6/25/2024) |
| Character of income at sale | No sale, so nothing yet | Ordinary income equal to the difference between the exercise price and FMV of the stock on the date of exercise (IRS Publication 5992, rev. 6/25/2024) | Capital gain or loss on disposition (IRS Publication 5992, rev. 6/25/2024) |
| 2026 AMT exemption in play | Yes. $90,100 unmarried, $140,200 joint, phasing out from $500,000 and $1,000,000 (IRS IR-2025-103, TY 2026) | Generally not, since no ISO adjustment arises | Yes, in the exercise year, at the same 2026 amounts |
| Where the tax payment comes from | Somewhere other than the shares. There are no sale proceeds | The sale itself | Sale proceeds arrive later than the AMT does |
That last row is the whole argument. The disqualifying disposition costs you the capital gain rate and hands you ordinary income, but it also hands you proceeds in the same year the tax is created. Exercise-and-hold buys the better rate and asks you to fund the tax from somewhere else entirely, on a share you cannot sell.
The $100,000 limit that decides how much is even an ISO
Before any of the above applies, there is a ceiling on how much of your grant gets ISO treatment at all. There is a $100,000 annual limitation on the value of an employee's ISO that may become exercisable for the first time during any calendar year, under IRC section 422(d), measured by fair market value at the time the option was granted rather than at vesting (IRS Publication 5992, revision date June 25, 2024). Anything above that limit is treated as a non-statutory option, with the ordinary income and employment tax rules that come with it.
So a grant you have always described as "my ISOs" may be part ISO and part NSO, split by a calendar-year test you never see on a statement. Worth confirming against your grant documents and your equity administrator's records with your CPA, rather than assuming the label on the offer letter still applies.
Why this comes up more in biotech than in big tech
A quick caveat on that framing, because it gets overstated. Whether a company grants options or RSUs tracks its funding stage more than its industry, and plenty of San Diego biotechs switch to RSUs once they are public or late-stage. What is fair to say is narrower: option grants remain common at earlier-stage companies, and this county has a lot of them. RSUs are taxed as ordinary income at vest with shares typically withheld to cover it, so the tax and the liquidity show up together. Options separate them, and at a private company they separate them by years. That gap between when the tax is created and when the shares can be sold is what our biotech and life-science planning page is built around, along with the concentration question sitting underneath it.
Next, the departure problem. Biotech careers move between companies, and most option agreements give a short window after termination to exercise or forfeit. That deadline does not care what the 409A did last quarter or what your AMT position looks like. It is also the moment a 401(k) tends to get left behind at the old employer, which is a separate and much simpler cleanup item covered in what to actually do with an old 401(k).
Lastly, concentration. Pre-IPO shares are not a position you can trim. They are not marginable in any ordinary sense, they may be subject to a right of first refusal, and their value is a board's periodic estimate rather than a market price. If most of your household balance sheet is one clinical-stage company's equity, the planning question is not really about tax at all. If you are wondering whether that even qualifies as something an advisor works with, we wrote about what asset level actually matters when working with a wealth manager, and illiquid equity is a real part of that conversation.
Items to take to your CPA before the year closes
- Confirm with your CPA which tranches of your grant are ISO and which spilled over the $100,000 annual limit into non-statutory treatment.
- Evaluate with your CPA what bargain element your current 409A or market price would produce, and where that lands against the 2026 exemption and phase-out amounts.
- Confirm the exact grant dates and any prior partial exercises, since the 2-year and 1-year clocks run from different events.
- Review your grant agreement with your attorney or equity administrator for post-termination exercise windows, transfer restrictions, and any right of first refusal.
- Discuss with your CPA and advisor how any AMT would be funded, given that an exercise-and-hold produces no proceeds.
None of those are a strategy. They are the inputs a strategy would need, and the answers differ enough between two people at the same company that a general rule here would be worth very little.
Frequently asked questions
Does exercising an ISO trigger a tax bill right away?
Not for regular tax. The IRS states that no income is recognized for regular tax when an ISO is exercised. But the bargain element is an adjustment on Form 6251 for the alternative minimum tax in the exercise year, so an AMT liability may arise even though nothing was sold (Instructions for Form 6251, 2025).
What exactly is the bargain element?
It is the fair market value of the stock acquired through the exercise minus the amount you paid for it, including anything paid for the option itself. Your Form 3921 from the employer reports the dates and values used to figure it (IRS Topic No. 427, reviewed April 28, 2026).
How much can I exercise before AMT becomes a factor?
There is no single number, because the AMT calculation runs against your whole return. The 2026 exemption is $90,100 for unmarried filers and $140,200 for joint filers, beginning to phase out at $500,000 and $1,000,000 respectively (IRS IR-2025-103, October 9, 2025). Where your other income already sits inside that range is what determines the answer, and it is a calculation for your CPA.
Is a disqualifying disposition always the wrong move?
No. It converts what could have been capital gain into ordinary income, but if you exercise and dispose of the stock in the same year, regular tax and AMT treatment are the same and no ISO adjustment is required (Instructions for Form 6251, 2025). It also produces proceeds in the same year the tax is created. That is a real tradeoff, not a mistake.
My company is private and I cannot sell the shares. Does the AMT still apply?
The AMT adjustment is driven by fair market value at exercise, not by whether a market exists to sell into. That is the core of the timing mismatch for pre-IPO holders, and it is the reason the funding question is worth working through with a CPA and an advisor before an exercise rather than after.
If you are holding ISOs and the year is closing
The exercise decision and the concentration decision are two separate planning topics, and running them together is how people end up with an AMT surprise and a position they never chose to hold. Our biotech and life-science planning page covers both, alongside your CPA rather than instead of them. Fee is discussed during a complimentary review. Do you want to look at your exercise year before it closes?
This material is provided for educational and informational purposes only and is not intended as a recommendation to exercise, hold, sell, or otherwise transact in any security or equity compensation arrangement. The tax treatment of incentive stock options (ISOs), alternative minimum tax (AMT), and equity compensation strategies can vary significantly based on individual circumstances. Examples contained herein are hypothetical and are intended solely to illustrate general concepts. Actual results will vary. Tax laws, IRS guidance, and equity compensation rules are subject to change. Consult a qualified tax advisor, attorney, and financial professional before implementing any strategy discussed.