Stock Options Tax Guide: ISO vs NSO, AMT, and the 83(b) Election

Before exercising employee stock options, budget for both the share purchase and the resulting taxes. With private-company stock, you may have to fund both costs while waiting for an opportunity to sell. ISO holders need an AMT calculation; NSO holders need a compensation-income and withholding calculation.

The examples below use 2026 federal rules and hypothetical grants. Give your tax preparer the grant documents, exercise dates and share valuations so the calculation also includes your other income and state taxes.

Identify the grant before calculating tax

Keep a separate row for each grant with its option type, grant date, strike price, vesting schedule, expiration date, shares already exercised, and remaining shares. Obtain the company’s exercise-date valuation and any restrictions on transferring stock. Use the valuation applicable to the exercise date.

Question	Incentive stock option, or ISO	Nonstatutory option, often called NSO or NQSO
Typical tax event at exercise	Generally no regular income tax, but an AMT adjustment may arise	For the usual option without a readily determinable market value at grant, compensation income generally arises at exercise
What matters at sale?	Whether both statutory holding periods were satisfied	Sale proceeds compared with adjusted stock basis
Main planning problem	Paying tax while holding shares that may be illiquid	Funding exercise cost and tax withholding, then recording correct basis

The IRS stock-option overview distinguishes the two treatments. NSOs generally enter the calculation through compensation income; ISO exercises can create a separate AMT adjustment.

ISO qualification has several separate clocks

Under Section 422, favorable sale treatment generally requires holding the stock beyond both two years from the option grant and one year from the stock transfer at exercise. The one-year stock holding period starts at exercise.

The $100,000 annual ISO limitation uses the stock’s grant-date fair market value for options first exercisable in a calendar year, across the relevant employer and related-company plans. Excess options receive non-ISO treatment under the statutory ordering rule.

Employment also matters. The usual qualification rule measures continuous employment through three months before exercise, with exceptions including a longer period for qualifying disability. Your contract may set a shorter exercise window, so check its post-termination deadline immediately when leaving a job.

For planning, place grant, exercise, qualifying-sale, and contractual expiration dates on one calendar. A tax-efficient sale date is irrelevant if the option expires before you exercise it or company restrictions prevent the intended sale.

Calculate the exercise’s AMT cost

The Form 6251 instructions explain the ISO adjustment and separate regular-tax and AMT bases. For ordinary vested shares retained after exercise, the spread is generally the exercise-date value minus what you paid. Restricted shares require additional analysis of when rights become transferable or cease being subject to substantial forfeiture risk.

The IRS’s 2026 inflation adjustments set these AMT amounts:

Filing status	Exemption before phaseout	Taxable excess above which the 28% rate starts
Unmarried individual other than a surviving spouse	$90,100	$244,500
Married filing jointly or surviving spouse	$140,200	$244,500
Married filing separately	$70,100	$122,250

The rate below that breakpoint is 26%. For 2026, the exemption begins phasing out at $500,000 of AMT income for unmarried filers and $1 million for joint filers, falling by 50 cents for each additional dollar above the threshold. It reaches zero at $680,200 and $1,280,400 respectively. For example, a single filer with $550,000 of AMT income has a $65,100 exemption: $90,100 minus 50% of the $50,000 excess. The AMT statute sets the phaseout rate; the IRS table supplies the 2026 amounts. Preferential capital-gain rates can also affect the computation.

Consider 10,000 ISO shares with a $5 strike and a $25 exercise-date value. The exercise costs $50,000, and the spread is $200,000. Assume an unmarried taxpayer has $150,000 of AMT income before exercise, all relevant income receives ordinary rates, the exemption is fully available, the regular-tax comparison amount is $25,000, and there are no other adjustments or credits:

1. AMT income after exercise is $350,000.
2. Subtracting $90,100 leaves $259,900 of taxable excess.
3. The tentative minimum tax is $244,500 × 26% plus $15,400 × 28%, or $67,882.
4. Subtract the assumed $25,000 regular-tax amount: additional AMT is $42,882.

The combined exercise cost and additional AMT in this scenario is $92,882, before state tax. Keep both amounts in your cash plan and recalculate them if the exercise-date value changes.

Selling sooner can reduce one risk while changing tax treatment

An ISO sale before both holding periods expire is a disqualifying disposition. Compensation-income rules then apply; a loss sale can have different limits from a profitable sale. Have the preparer reconcile the exercise value, sale proceeds and holding periods.

If ISO shares are exercised and disposed of in the same tax year, the IRS says their regular-tax and AMT treatment is the same and no ISO adjustment is required. Include any unrelated AMT adjustments elsewhere on the return.

Compare two cash plans: exercising and retaining every share versus selling enough permitted shares to cover exercise and taxes. The first retains more upside but exposes more household cash to one employer. The second may sacrifice favorable holding-period treatment while making the tax bill fundable. Include a falling-share-price scenario and a scenario where no sale is available.

AMT paid on deferral items can generate a future minimum tax credit under Form 8801. The amount usable each year depends on the credit rules and that year’s return. Treat recovery as a future tax benefit when available, rather than cash available for the exercise. Preserve Form 3921, exercise confirmations, AMT basis schedules, and credit carryforwards.

NSO basis prevents the same income being counted twice

Suppose you exercise 5,000 NSOs at $10 when the shares are worth $30. You pay $50,000, recognize $100,000 of compensation, and have $150,000 of stock basis, assuming the ordinary exercise rules apply. Employee compensation is generally reported through payroll. Compare the amount withheld with the projected total liability to determine whether an additional payment is needed.

If those shares later sell for $35 each, proceeds are $175,000 and the capital gain is $25,000 before fees. Reporting only the $50,000 purchase cost as basis would overstate that gain by the compensation already recognized.

Publication 525 warns that broker basis reporting for options granted on or after January 1, 2014, does not include the compensation component. Reconcile the W-2, broker supplemental statement, and Form 1099-B; use Form 8949 adjustments where required. Whether the subsequent capital gain is long-term depends on the stock holding period.

An 83(b) election concerns transferred property

An 83(b) election can apply when substantially nonvested stock is transferred for services. The election requires an actual transfer of property, so confirm when shares were transferred and which vesting restrictions remain. For early-exercised ISO shares, have the preparer also apply the separate AMT rules.

Form 15620 records the property, transfer date, restrictions, value, and amount paid. Filing is generally due no later than 30 days after transfer; the instructions specify the weekend and legal-holiday postmark rule. Give the required copy to the service recipient, follow current filing instructions, and retain proof. Revocation requires IRS consent.

For a simple restricted-stock purchase, assume 100,000 shares are worth $0.10 each and you pay $0.10 each. The purchase costs $10,000; the value-minus-price amount included through the election is zero. If the same shares were transferred free, that difference would instead be $10,000.

The attraction is fixing compensation value while it is low. The risk is paying for stock or paying tax before knowing whether the shares will vest or retain value. Publication 525 explains that forfeiture does not simply refund tax on income previously included through an election. Keep this exposure separate from emergency savings.

Check QSBS separately from ISO status

Qualified small business stock treatment under Section 1202 has issuer, acquisition, active-business, holding-period, and other conditions. Ask the issuer for records supporting those conditions.

For eligible stock acquired after July 4, 2025, the statute provides 50%, 75%, and 100% gain exclusions at the three-, four-, and five-year holding points. It also introduces the $15 million per-issuer gain limit, subject to the alternative ten-times-basis limitation and prior exclusions, and a $75 million issuer gross-assets threshold for qualifying new issuances. Earlier stock follows different transition rules. Apply the exclusion to eligible gain after confirming the stock’s acquisition date and issuer qualification.

Preserve the issuer documentation and the date you acquired the stock. Then coordinate federal treatment with the state income-tax guide and your broader investment plan. A tax benefit is useful only if the stock, cash requirements, and concentration risk fit that plan.

Sources

• IRS: Tax Topic 427, stock options
• U.S. Code: Section 422, incentive stock options
• IRS: Form 6251 instructions
• IRS: 2026 inflation adjustments, Revenue Procedure 2025-32
• IRS: Form 8801 instructions
• IRS: Publication 525, taxable and nontaxable income
• IRS: Form 15620 and 83(b) instructions
• U.S. Code: Section 1202, qualified small business stock