Stock Options Taxed

How Are Stock Options Taxed? The Employer's Answer

Stock options are taxed by type. An NSO exercised on vested shares is taxed as wages at exercise, with withholding due for an employee. An ISO is taxed at sale for regular federal income tax, and its exercise spread can enter the alternative minimum tax calculation in between.

Written by the

Slice Global equity team

Last updated

October 2026

TL;DR

The short version, by stage.

Grant: no tax on a standard option struck at or above fair market value.

Exercise: for vested shares, an employee's NSO spread is wages with withholding due. A US contractor's spread is generally 1099-NEC income with no wage withholding. An ISO spread carries no regular federal income tax, but for vested shares held past the exercise year it enters the AMT calculation.

Sale: capital treatment on growth after exercise, long-term once held more than a year. An ISO that keeps both holding periods turns the whole gain over the strike into long-term capital gain.

The employer's job: withholding and code V on employee NSO exercises, wage reporting on RSU deliveries, and Form 3921 for each reportable ISO share transfer by a current or former employee.

The question arrives with a deadline attached: an employee has 90 days left to exercise after leaving, or a tender offer closes Friday, and they want to know what the tax will be. The answer depends on whether the option qualifies as an ISO, not on the label in the grant agreement. ISOs and NSOs look interchangeable in an offer letter and are taxed on different schedules.

This guide covers how each option type is taxed, stage by stage from grant to sale, how partial sales of an ISO exercise work, what the 2026 AMT numbers do to the ISO math, and the three jobs the employer carries.

How stock options are taxed: ISO vs NSO at a glance

The two US tax categories for compensatory options are ISOs and NSOs, and the category decides when federal income tax lands:

ISO

NSO

Who can hold it

Employees only, and ISO status has conditions: a stockholder-approved plan, a strike never below grant-date fair market value (110 percent for a holder of more than 10 percent of the voting power), a 10-year maximum term (5 years for that holder), and continuous employment from the grant date through to 3 months before exercise, extended to 1 year where the termination is for disability. Fail a qualification or employment condition and the exercise is taxed as an NSO; fail a holding period after exercise and the sale is a disqualifying disposition, with ordinary income at that sale

Anyone: employees, advisors, contractors, directors

Tax at exercise

None for regular federal income tax; the spread is an AMT adjustment under Section 56(b)(3) for vested shares held past the exercise year

Employees: spread taxed as wages, withholding due. US contractors: generally 1099-NEC income, no wage withholding, no FICA

Tax at sale

Long-term capital gain on the whole gain over the strike, if held 2 years from grant and more than 1 year from exercise

Capital treatment only on growth after exercise

Employer deduction

None, unless a disqualifying disposition moves income into wages

Yes, generally the amount the holder includes, in the matching year, subject to the usual deduction rules

The limitation

The $100K limit: grant-date value of ISOs first exercisable in a calendar year, counted in grant order across plans of the employer and its parent and subsidiaries, measured at grant. The excess is an NSO

Tax for the employee at exercise, on shares that may not be sellable

The full comparison, including the employer side, is in ISO vs NSO tax (coming soon).

Stock option tax at grant, vesting, exercise and sale

A standard option is taxed at exercise, at sale, or both; grant and vesting stay quiet unless the option is discounted or early-exercised.

At grant: nothing for a standard option, meaning a strike at or above grant-date fair market value, no readily ascertainable value for the option itself, and no discount. A discounted compensatory option that is subject to Section 409A generally fails the stock-right exemption, and if it does not comply, the holder can face income at vesting, a 20 percent additional federal tax and premium interest.

At vesting: still nothing for options that have not been exercised. Shares from an early exercise are different: without a timely 83(b) election, the income for an NSO, or the AMT adjustment for an ISO, arises as the shares vest. The 83(b) clock runs 30 days from the transfer of the restricted shares, ordinarily the early exercise, not from vesting and not from grant, covered in the 83(b) election guide.

At exercise: for an employee's NSOs, payroll treats the spread like a bonus:

Federal income tax withholding at 22 percent under the flat-rate method, where the employer is eligible to use it; otherwise the aggregate method.
A mandatory 37 percent on the excess over $1,000,000 of supplemental wages in the year, regardless of the W-4.
Social Security up to the $184,500 wage base, plus Medicare.
State income tax where it applies.

An independent contractor's or nonemployee advisor's NSO exercise is generally not wages if the award was earned for nonemployee services: no wage withholding, no FICA, and the spread generally lands on a Form 1099-NEC, though backup withholding can apply. A former employee's exercise of an option earned in employment stays W-2 compensation.

ISO exercises carry no withholding and no FICA. The employer's job there is a Form 3921 for each reportable share transfer on exercise, one form per transaction, subject to the nonresident alien exception. An option cashed out rather than exercised is compensation through payroll, with no Form 3921.

At sale: capital treatment on the growth after exercise, short-term at one year or less, long-term once held more than a year. An ISO that keeps both holding periods turns the entire gain, strike to sale price, into long-term capital gain. Sell early and the disqualifying disposition rules generally pull the spread into W-2 box 1 for the year of sale, with no income tax withholding and no FICA.

Partial sales of an ISO exercise: why one sale does not disqualify all of it

Employees can fund an exercise by selling some of the shares, either through a broker sale or by having the company withhold shares to cover the cost. Where net exercise was in the option's original terms, advisers commonly split the shares two ways:

The sold or withheld shares: a disqualifying disposition, taxed as ordinary income.
The remaining shares: they can retain ISO treatment if the other conditions are met, and keep their AMT exposure.

The Code and regulations do not expressly settle this, so it is adviser practice rather than statute. The mistake is treating the whole exercise as disqualified because part of it was sold.

The 2026 AMT numbers and the ISO exercise

The AMT is the parallel federal tax system that recalculates income with fewer breaks, and the ISO spread on vested shares held past the exercise year counts there in full. The 2026 figures decide who reaches it:

Filing status

2026 exemption

Phase-out starts above AMTI of

Exemption gone at

Exemption

$90,100

$140,200

$70,100

Single

$90,100

$500,000

$680,200

Married filing jointly

$140,200

$1,000,000 (frozen through 2026)

$1,280,400

Married filing separately

$70,100

$500,000

$640,200

The exemption shrinks by 50 cents for each dollar of AMTI above the floor, so once AMTI passes the floor, a large spread adds AMT income and can reduce the exemption that would have absorbed it.

Run the calculation both ways before setting an exercise date. The Equity Value Simulator estimates tax outcomes for planning; its estimates are informational, not tax advice. The full mechanics are in the AMT and stock options guide.

What softens the AMT hit, three mechanics:

A sale in the exercise year generally prevents the exercise-year AMT adjustment on the shares sold; retained shares are analyzed separately.
AMT paid on the ISO adjustment can generate a minimum tax credit under Section 53, claimed on Form 8801 against regular tax in later years, within that form's limits.
The shares carry a higher AMT basis than their regular-tax basis, which shrinks the AMT gain when they are eventually sold.

One thing that does not soften it: a large qualifying sale can create AMT exposure of its own in a high-income year, because the gain lifts AMT income into the phase-out band. The dual basis shrinks that exposure without always removing it.

What the employer does for stock option taxes: three jobs

The tax is the holder's, but three jobs sit with the company.

One: withhold correctly on employee NSO exercises and RSU deliveries. Independent contractors generally have no wage withholding on an NSO exercise, though backup withholding can apply; an option earned during employment can stay subject to wage withholding when a former employee exercises it.

Two: report. Code V in W-2 box 12 for employee NSO spreads. Form 3921 for each ISO share transfer by a current or former employee, apart from the nonresident alien exception, on three deadlines:

Employee copies by January 31.
IRS filing by February 28 on paper.
Or March 31 electronically, and e-filing is mandatory at 10 or more information returns in aggregate.

Penalties run $60 to $340 per return, and at least $680 with no cap where the failure is intentional disregard.

The form also feeds the employee's own return. The ISO spread never appears on the W-2 at exercise; the employee or their tax preparer takes the grant date, exercise date, strike, fair market value and share count from the 3921 to Form 6251 and tests whether AMT is due. The employee copy, due January 31, is the input to the holder's own return.

A disqualifying disposition is W-2 box 1 wages only: no withholding, no FICA, no code V. The company may need its own way to learn of the disposition.

Three: keep the 409A presumption alive. A qualifying independent appraisal is presumed reasonable for 12 months, or until material new information affects the valuation, whichever comes first. Grant off an older or overtaken valuation and those strikes are open to challenge.

Practice note. The 22 percent flat rate is fixed by regulation. An employer cannot dial it up, and it covers federal income tax only: Social Security and Medicare still apply on top and cannot be waived. What an employer can run instead is the aggregate method. What an employee can do is file a W-4 with additional withholding; for underpayment purposes, withholding is generally treated as paid evenly across the year unless actual dates are established, so whether it cures an earlier shortfall depends on the calculation.

Where Slice fits

Stock option tax runs on records: which grants are ISOs, when each exercise happened, and what the shares were worth that day. Kept in spreadsheets, those records drift. Slice flags a grant that crosses the $100K ISO limit, displays the ISO/NSO breakdown, and provides an ISO/NSO Split Grants ($100K Threshold) report.

For NSO exercises, Slice captures and tracks withholding through the exercise workflow; for ISO exercises, it prepares the Form 3921 data for filing.

The same record covers grants in 67+ countries, so US options sit beside awards that other countries tax on their own schedules. Your team enters or approves every fact, and filing stays in your hands.

FAQ

Frequently asked questions

Are stock options taxed when they are granted?

No, if the option is standard: a strike at or above grant-date fair market value, no readily ascertainable fair market value for the option itself, and no discount. Regular federal income tax arrives at exercise for NSOs, or at sale for ISOs that keep their holding periods, and the AMT can reach an ISO spread at exercise. The exception is a discounted option, which can fall under Section 409A.

How much tax is withheld when an employee exercises NSOs?

Four pieces, for an employee:

Federal income tax at 22 percent under the flat-rate method where the employer is eligible to use it (otherwise the aggregate method), and a mandatory 37 percent on the excess over $1,000,000 of supplemental wages, regardless of the W-4.
Social Security, up to the $184,500 wage base for 2026.
Medicare, plus the additional 0.9 percent above $200,000.
State income tax where applicable.

The spread lands in W-2 wages with code V. A US contractor's exercise takes no wage withholding: the spread generally goes on a Form 1099-NEC, though backup withholding can apply.

What is a disqualifying disposition?

A sale of ISO shares before holding them 2 years from grant and more than 1 year from exercise. The sale generally converts the spread into ordinary income for the year of sale, reported in W-2 box 1, with no income tax withholding, no FICA and no code V; if an arm's-length sale lands below the exercise-date value, the ordinary income is limited to the actual gain.

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A disqualifying disposition can also give the employer a deduction, subject to the usual rules.

Do ISOs avoid tax at exercise?

For regular federal income tax, yes. For the AMT, no: for vested shares held past the exercise year, the spread at exercise is an AMT adjustment under Section 56(b)(3). Two reliefs exist: a sale in the exercise year generally prevents the adjustment on the shares sold, and AMT paid on it can generate a credit claimed in later years on Form 8801, within that form's limits.

Is stock option tax different for employees outside the US?

Yes. Each country taxes options on its own schedule, and many run named regimes with their own conditions; the country guides are in the global equity hub. One US detail: no Form 3921 is required for an exercise by a nonresident alien who needs no W-2 from the company for any year from the grant year through the exercise year.