IRC 422: ISO Holding Periods, AMT, and the $100,000 Rule

Incentive stock option tax rules give you a shot at paying long-term capital gains rates (topping out at 20%) on the entire profit from your options, instead of ordinary income rates that reach 37%. To earn that treatment you have to clear two holding periods after exercise, stay inside a tight post-employment window, and survive the alternative minimum tax that can hit the year you exercise. Miss any of those and part or all of your gain shifts back into ordinary income.

The Two Holding Periods That Unlock Capital Gains Rates

A qualifying disposition is what converts your whole profit into a long-term capital gain. You get there by satisfying both of the following after you exercise:

Two years from the grant date. You cannot sell until at least two full years after the company originally granted you the option.
One year from the exercise date. You must also hold the shares for at least one year after you exercised and took ownership.

Both clocks must run out. A sale on or after the later of the two dates qualifies.¹

The tax treatment along the way: you owe nothing at grant, and nothing for regular income tax purposes when you exercise, even if the stock has climbed well above your exercise price.² When you finally sell in a qualifying disposition, the entire difference between your sale price and your original exercise price is a long-term capital gain.

Put numbers on it. Say you received an ISO to buy 1,000 shares at $10 each. You exercise when the stock trades at $50, spending $10,000. After both holding periods are done you sell for $70. Your taxable gain is $60,000 ($70,000 in proceeds minus your $10,000 cost), all taxed at long-term capital gains rates of 0%, 15%, or 20% depending on your total taxable income.³

High earners should budget for an additional 3.8% Net Investment Income Tax on top of the capital gains rate. NIIT kicks in when modified adjusted gross income exceeds $200,000 for single filers or $250,000 for married couples filing jointly, and those thresholds are not indexed for inflation.⁴

Sell those same shares at $25 instead, below the $30 exercise-date FMV, and your ordinary income is capped at $15 (your real gain), with no capital gain component.

The AMT Trap at Exercise

The alternative minimum tax is where ISO planning gets genuinely dangerous. For regular tax purposes, exercising creates no taxable event. For AMT purposes, the bargain element (exercise-date FMV minus your exercise price) is added to income as a positive adjustment.⁶ If that pushes your alternative minimum taxable income above the AMT exemption, you owe the higher of your regular tax or the tentative minimum tax.

For 2026, the AMT exemption is $90,100 for single filers and $140,200 for married couples filing jointly, phasing out starting at $500,000 (single) and $1,000,000 (joint). The rate is 26% on the first $244,500 of AMT-taxable income above the exemption, then 28%.⁷

The numbers can be startling. Exercise an ISO at $10 when the stock is worth $110, and you have a $100-per-share bargain element. On 5,000 shares that’s a $500,000 AMT adjustment and a potential AMT bill of $100,000 or more, on stock you haven’t sold and may not be able to sell. During the dot-com bust, employees exercised into rapidly appreciating stock, owed enormous AMT bills, and then watched the stock collapse before they could sell. They owed tax on gains that no longer existed.

The AMT Credit

AMT paid on an ISO exercise creates a credit you can recover in future years, applied in any year where your regular tax exceeds your AMT. The credit works with a dual-basis system: your AMT basis is the higher exercise-date FMV, your regular-tax basis is the lower exercise price, and the difference prevents the same spread from being taxed twice when you eventually sell.

There’s no guarantee you’ll recover the full credit quickly. If the stock falls and you sell at a loss, you’ve permanently overpaid relative to your real gain. The credit can take years to unwind if you remain in AMT territory.

Exercise and Sell in the Same Year

If you exercise and sell in the same calendar year, the AMT adjustment and the sale cancel out for AMT purposes. The catch is that selling in the same year means you haven’t met the one-year post-exercise holding period, so the sale is a disqualifying disposition and you owe ordinary income tax on the spread.

That’s the central trade-off. Hold for qualifying-disposition treatment and risk an AMT hit plus a potential stock decline, or sell right away, skip the AMT problem, and accept ordinary income on the gain. The right answer depends on the size of the bargain element, your other AMT exposure, the stock’s volatility, and whether you can pay the AMT bill from other funds. Model the scenarios before you exercise; afterward, the year’s adjustment is locked in.

You Only Have Three Months After Leaving Your Job

An ISO must be exercised while you’re still employed by the granting company (or its parent or subsidiary), or within three months after employment ends.¹ After that window closes, unexercised options lose ISO status. If you leave a job with vested ISOs, the clock starts immediately.

One exception: if employment ends because of permanent and total disability, the window extends to one year.¹ Many company plans allow a longer post-termination exercise period, but any exercise after the three-month (or one-year) statutory window is treated as a non-qualified option exercise for tax purposes, regardless of what the plan says.

The $100,000 Rule You May Not Know Applies to You

The total FMV of stock underlying ISOs that become exercisable for the first time in any single calendar year cannot exceed $100,000, measured using the FMV on each option’s original grant date, not the current market price.⁸ The limit applies across all ISO plans from the same employer and its parent or subsidiary companies.

When options exceed the cap, earliest-granted options count first, and any excess automatically converts to non-qualified stock options with less favorable tax treatment. The rule looks at when options first become exercisable (the vesting date), not when you exercise. A company that front-loads vesting can push you over the cap and convert part of your ISO grants into NQSOs without anyone noticing until tax season.

What Your Employer Reports and What You Owe

When you exercise an ISO, your employer files Form 3921 with the IRS and gives you a copy by January 31 of the following year. It shows the grant date, exercise date, exercise price per share, FMV per share on the exercise date, and the number of shares transferred.⁹ You need this to calculate your AMT adjustment and, later, your gain or loss on sale.

If you make a disqualifying disposition, your employer reports the ordinary income portion in Box 1 of your Form W-2 with your regular wages. Here’s the catch that surprises people: the employer does not withhold federal income tax or FICA on that income. You cover the full liability yourself, through estimated tax payments or by adjusting withholding on other compensation. Skip that step and you can end up with an underpayment penalty on top of the tax.

Special Situations

Death

If you die before exercising ISOs, or before meeting the holding periods on exercised shares, your estate or heirs get the favorable tax treatment under Section 421(a) without needing to satisfy the two-year and one-year periods or the employment requirement.¹⁰

Mergers and Acquisitions

If your employer is acquired or merged, your ISOs don’t automatically lose their status. The acquiring company can substitute new options or assume the existing ones, and ISO treatment survives if the aggregate spread doesn’t increase and the new or assumed option provides no benefit the original didn’t.¹¹

In practice, acquirers often cash out existing options at closing. If your ISOs are cashed out and you haven’t met both holding periods, that’s a disqualifying disposition: ordinary income on the spread. You rarely get to opt out. If you hold significant unrealized ISO gains and hear acquisition rumors, model the tax hit from a forced early disposition before the deal closes.

1
Office of the Law Revision Counsel. 26 US Code 422 – Incentive Stock Options
2
Office of the Law Revision Counsel. 26 US Code 421 – General Rules
3
Internal Revenue Service. Topic No. 409, Capital Gains and Losses
4
Internal Revenue Service. Topic No. 427, Stock Options
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Office of the Law Revision Counsel. 26 US Code 56 – Adjustments in Computing Alternative Minimum Taxable Income
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Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026
8
eCFR. 26 CFR 1.422-4 – $100,000 Limitation for Incentive Stock Options
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Internal Revenue Service. Instructions for Forms 3921 and 3922
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Office of the Law Revision Counsel. 26 USC 421 General Rules
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Office of the Law Revision Counsel. 26 US Code 424 – Definitions and Special Rules