ISO vs. NSO Taxation: Exercise, AMT, Qualifying Dispositions & 83(b)

Updated for tax year 2026 · 9 min read

Both kinds of stock option give you the right to buy shares at a fixed strike price — but the IRS treats them as two different animals. A non-qualified stock option (NSO) creates salary income the day you exercise, full stop. An incentive stock option (ISO) can skip that tax entirely if you hold long enough — at the price of a possible Alternative Minimum Tax (AMT) bill in the exercise year. Same grant, opposite planning problems. Here is how each one actually works, with one example carried through every scenario.

The one example we'll use throughout

Nothing is taxed at grant for either type, and nothing is taxed as options vest. All the action is at exercise and at sale.

NSO: taxed at exercise, no exceptions

Exercise an NSO and the bargain element is ordinary wage income that day — it lands in Box 1 of your W-2, your employer withholds on it (flat 22% federal supplemental rate, plus state), and it is also subject to Social Security and Medicare taxes like any other wages. This happens whether you sell the shares or hold them. That last part is the NSO trap: exercise-and-hold in a stock that later falls, and you still owe full tax on a bargain element that no longer exists.

When you eventually sell, only the growth after exercise is a capital gain — your basis is the exercise-date price. Sold more than a year after exercise, it's long-term.

ISO: no regular tax at exercise — but watch the AMT

Exercise an ISO and hold the shares, and there is no regular income tax and no withholding at exercise. That sounds like a free lunch, and for regular tax it is. The catch: the bargain element is an adjustment for the Alternative Minimum Tax. Your AMT income for the exercise year includes that $16,000, and if your tentative minimum tax (computed at 26%/28% AMT rates above an exemption) exceeds your regular tax, you pay the difference — in cash, in the exercise year, on shares you haven't sold.

On the example, if the full $16,000 adjustment were taxed at 26%, the rough AMT exposure is about $4,160 — on top of the $8,000 exercise cost. Whether you actually owe AMT depends on your whole return: salary level, the exemption, and how close your regular tax already is to the AMT line. Small exercises often owe nothing; large ones at high salaries are where AMT bites. This is why ISO exercises are sized deliberately — exercising in tranches across tax years, or early in a low-income year, keeps each year's adjustment manageable.

Two mercies: a disqualifying sale in the same year as the exercise wipes out the AMT adjustment entirely (the income becomes regular salary instead), and AMT paid on an ISO exercise generally comes back later as a minimum tax credit (Form 8801) in years when your regular tax exceeds your AMT. Keep your exercise paperwork forever — you'll also carry two different cost bases (regular-tax basis = strike; AMT basis = exercise-date price) until you sell.

The sale: qualifying vs. disqualifying dispositions

An ISO sale is qualifying if you sell at least 2 years after the grant date AND at least 1 year after exercise. Miss either date and the sale is disqualifying.

• Qualifying: no ordinary income at all. The entire gain over the strike is a long-term capital gain. On the example: ($165 − $40) × 200 = $25,000 × 24.3% = $6,075 total tax — the best outcome available, bought with two years of patience and stock risk.
• Disqualifying: the bargain element (capped at your actual gain over the strike, if the stock fell) becomes ordinary income, exactly like an NSO, and only growth after exercise is a capital gain. Sell within a year of exercise and that piece is short-term too: on the example, $6,608 + ($9,000 × 41.3%) = $10,325 — the worst outcome. Hold past the 1-year exercise mark but miss the grant date, and the capital piece turns long-term: $8,795, identical to the NSO result.

*Federal + California at the example's rates, before any AMT (ISO rows) or payroll taxes (NSO row). Same shares, same prices — a $4,250 spread driven purely by option type and sale timing.

83(b) elections: only for early exercise

An 83(b) election has nothing to do with ordinary vested options. It applies when your plan lets you exercise unvested options and receive restricted stock that vests over time. Normally you'd be taxed as each tranche vests, on whatever the bargain element has grown to. Filing an 83(b) within 30 days of exercise flips that: you're taxed once, immediately, on today's bargain element — often near $0 at a startup where strike ≈ current value — and everything after that is capital gain, with your holding clock starting now.

• The deadline is absolute: 30 calendar days from exercise, no extensions, no exceptions. Miss it and the election doesn't exist.
• It's irrevocable and it's a bet: if you leave and forfeit the shares, the tax you prepaid is gone — there's no refund and no loss deduction for the amount taxed.
• It does nothing for ISOs' AMT beyond the same early-tax trade, and it cannot be used for RSUs — no property is transferred at RSU grant, so there's nothing to elect on.

Most public-company employees will never file one. Most startup employees who early-exercise should at least ask the question within their first 30 days.

Fine print that changes real outcomes

• The $100,000 rule: ISOs lose their status on any shares first exercisable in a calendar year worth more than $100,000 (valued at grant). The excess is treated as NSOs automatically — large grants are often part ISO, part NSO without anyone telling you.
• Leaving your job: ISOs generally must be exercised within 90 days of your last day to keep ISO treatment; exercise later and they convert to NSO treatment. NSOs follow whatever exercise window your plan allows.
• States diverge: most states follow the federal ISO treatment, but California and New Jersey run their own ISO adjustments for state AMT purposes — a qualifying disposition federally isn't always the final word on your state return.
• Concentration: every strategy above requires holding a single stock longer. The tax saving on the example ($2,720 vs. an NSO) is real — and so is the risk of the position falling by more than that while you wait. Tax should size the hold, not dictate it.

ISO / NSO FAQ

How do I know which type I have?

Your grant agreement or your equity portal's option summary states it. If you were a contractor, they're NSOs — ISOs can only be granted to employees. If you can't find it, ask your company's stock admin before exercising; the tax treatment diverges too much to guess.

Can I avoid AMT by exercising ISOs in January?

Exercising early in the year doesn't change the AMT math, but it gives you information: if the stock collapses before December 31, a same-year disqualifying sale erases the AMT adjustment. Exercising in December removes that escape hatch.

Is the AMT I pay on ISOs just lost?

Usually not. It becomes a minimum tax credit carried forward on Form 8801, usable in later years when your regular tax exceeds your tentative AMT — which for most people is most years after the exercise year. It can take years to fully recover, which is a cash-flow cost, not a permanent one.

Should I always hold ISOs for a qualifying disposition?

No. Qualifying treatment saved $2,720 on the example versus the NSO path — worth having, but not worth holding a concentrated position through a downturn for. Run your own numbers, and weigh the tax delta against the risk of the shares themselves.