ISO or NSO, the two letters that decide what you keep

Jun 2026 · 5 min read

When your company hands you an option grant, it tells you four things. How many options, the strike price, the vesting schedule, and a two- or three-letter label. ISO or NSO. That label, plus a few timing decisions, is the difference between two executives holding the identical grant and walking away with very different net worth.

And in 2026 the stakes went up. The One Big Beautiful Bill Act quietly reset the alternative minimum tax so that large incentive-stock-option exercises sting more than they did last year.

The two engines

An ISO (incentive stock option, employees only) is the tax-favored one. Exercising it creates no regular taxable income. The "bargain element," the gap between the share's value at exercise and your strike, is invisible to regular tax. Hold long enough and the whole gain becomes long-term capital gain. "Long enough" means a qualifying disposition: sell no sooner than two years after grant and one year after exercise (IRC §422). Sell early and the benefit collapses into ordinary income.

An NSO (nonqualified) has no such conversion. The bargain element is ordinary compensation income the moment you exercise, on your W-2, with income-tax withholding and FICA. Your basis resets to the value at exercise, and only later appreciation is capital gain.

The ISO catch is AMT

That bargain element invisible to regular tax is fully visible to the alternative minimum tax. AMT is a parallel calculation, and you pay whichever is higher. So an exercise-and-hold ISO can hand you a tax bill on a gain you have not sold, on cash you do not have. Phantom income.

Here is what changed for 2026. The AMT exemption now starts phasing out at $500,000 of AMT income for singles and $1,000,000 for joint filers, and it phases out twice as fast as before, 50 cents on the dollar instead of 25 (OBBBA; Rev. Proc. 2025-32). A large exercise burns through the exemption faster, so more of the spread gets taxed.

What it looks like in numbers

Same $1.5M spread, two very different years. The ISO route owes the least over a lifetime if the stock holds and you reach a qualifying sale (the later gain taxes at roughly 23.8% instead of 37%). But it demands about $420,000 of AMT cash this year against zero proceeds. The NSO route costs more now and carries no holding risk. (Every AMT figure here is simplified; a real answer needs a full Form 6251 model.)

The edges that bite

None of these are forgiving:

• Holding periods. Two years from grant and one year from exercise. Miss either and it is a disqualifying disposition.
• The three-month rule. Leave your employer and exercise an ISO more than three months later and it is taxed as an NSO, whatever the plan says (IRC §422).
• §83(b), 30 days. On early-exercised unvested stock, filed within 30 days of transfer. For an early ISO exercise, an 83(b) election for AMT purposes fixes the AMT measurement to the exercise year (a regular-tax 83(b) generally cannot be made on ISO stock, but the AMT one can).
• The $100,000 limit. Only the first $100,000 of options (valued at grant) that first become exercisable in a year keep ISO status; the rest is automatically NSO (IRC §422(d)).

AMT is a prepayment, not a penalty

The piece executives miss: AMT you pay on an ISO comes back as a minimum tax credit (Form 8801), against your regular tax in later non-AMT years. But only if you can front the cash now. If the liquidity shock would break you, exercise-and-hold is the wrong move even when it looks optimal on paper.

This is where the pieces have to move together. We handle the tax side, running the Form 6251 crossover to find the largest exercise that keeps you under the phaseout and tracking your dual basis and AMT credit. Your equity-comp attorney confirms the grant type and the $100k split. And the cash for any AMT prepayment gets lined up in advance, not discovered at filing. State rules vary too, since several do not conform to federal AMT, so a mobile executive models state separately.

The framework is evergreen, but the 2026 AMT math is unforgiving and the deadlines are real. Running your real numbers, modeling the Form 6251 crossover, and timing the exercises is the kind of work we do for our clients. A Diagnostic is where it starts. It gives you a clear read on whether your spread, income, and liquidity put you in the danger zone this year, and what is worth planning before a deadline decides for you. Start your Diagnostic.

This article is general tax information, not specific tax advice. Your situation has details we cannot see from a blog post. Talk with us or your tax professional before acting on it.