Blog · 16 October 2026

ISO vs NQSO: Incentive Stock Options, AMT and Form 3921 for US CPA Firms

By Keshav Bansal, CA

Equity compensation questions reach every CPA firm, and most start with one: ISO vs NQSO — which kind of option did the client actually receive? Incentive stock options (ISOs) and nonqualified stock options (NQSOs) can cover the same shares at the same strike price and still be taxed very differently at exercise, at sale and under the AMT. A refresher published by law firm Haynes Boone on October 5, 2026 is a good prompt to revisit the rules and the places returns go wrong.

Statutory vs nonstatutory options

IRS Topic 427 (last reviewed September 24, 2026) sorts employee options into two groups. Options granted under an ISO plan or an employee stock purchase plan are statutory stock options; everything else is a nonstatutory stock option — what practitioners call an NQSO.

Eligibility is the first filter. Haynes Boone notes that ISOs can only be granted to employees of corporations; options granted to non-employee directors, contractors or employees of partnerships or LLCs are NQSOs. Publication 525 adds that the holder must be an employee of the granting company (or a related company) from grant until 3 months before exercise — 1 year for an ISO holder who is disabled — and the option must be nontransferable except at death.

What makes an option an ISO under §422

Section 422(b) requires a plan stating the aggregate number of shares and the eligible employees, approved by stockholders within 12 months before or after adoption. The option must be granted within 10 years of plan adoption or approval (whichever is earlier), must not be exercisable more than 10 years after grant, must have an exercise price of at least fair market value at grant, and must be transferable only by will or the laws of descent and distribution.

• 10% owners. A holder of more than 10 percent of the combined voting power qualifies only if the price is at least 110 percent of fair market value and the term is no more than 5 years (§422(c)(5)).
• $100,000 limit. To the extent the stock (valued at grant) under ISOs first exercisable in any calendar year exceeds $100,000, the excess options are treated as non-ISOs, in the order granted (§422(d)).
• Designation. An option is not an ISO if its terms say so, or if a §83(i) election is made. Haynes Boone adds that the award agreement must state ISO intent at grant; an employer cannot designate an ISO later.

How NQSOs are taxed

Most NQSOs have no readily determinable fair market value, so Topic 427 says there is no taxable event at grant; at exercise, the employee includes the stock’s fair market value less the amount paid. Section 83(e)(3) keeps §83 from applying to the grant of such an option, and Publication 525 says stock that is not yet substantially vested is taxed when it vests.

Publication 525 says the spread is reported in box 12 of Form W-2 with code V and included in boxes 1, 3 (up to the social security wage base) and 5. Under §83(h), the employer deducts the amount the employee includes. The employee’s basis is the price paid plus the income recognized.

How ISOs are taxed — and the AMT catch

Under §421(a), a qualifying ISO exercise produces no income, and the employer gets no §162 deduction. Section 422(a) requires that the employee not dispose of the shares within 2 years from grant or within 1 year after transfer. If both periods are met, Publication 525 treats the whole gain on sale as capital gain, with basis equal to the price paid.

The deferral does not carry over to the AMT. Section 56(b)(3) says §421 does not apply to ISO stock for AMT purposes. Publication 525 (2025) explains that the excess of fair market value over the option price — measured when the rights become transferable or no longer subject to a substantial risk of forfeiture — is an adjustment on Form 6251, line 2i, with a matching increase in AMT basis. No adjustment is needed if the stock is sold in the year of exercise. Regular and AMT basis will differ, so records are needed for both.

Disqualifying dispositions

A sale before either holding period ends is a disqualifying disposition. Per Publication 525, gain is ordinary income up to the spread at exercise, with any excess capital gain; a loss is a capital loss with no ordinary income. Section 422(c)(2) limits the ordinary amount to the gain realized when shares are sold below their exercise-date value in a sale on which a loss would be recognized. Section 421(b) puts the income, and any employer deduction, in the year of disposition and says no income tax withholding is required.

Haynes Boone flags two common triggers: selling right after exercise in a company sale, and net share settlement to cover the exercise price. The ordinary income should appear in W-2 box 1; if not, Publication 525 says the employee reports it as wages on Schedule 1 (Form 1040), line 8k.

Form 3921 and the basis trap

Under the Form 3921 instructions (Rev. April 2025), every corporation that transfers stock on an ISO exercise files Form 3921 for each transfer, showing grant date (box 1), exercise date (box 2), exercise price per share (box 3), fair market value per share at exercise (box 4) and shares transferred (box 5). Publication 525 notes that for 2025 exercises the form had to be provided by January 31, 2026.

The bigger risk is on the sale side. For options granted on or after January 1, 2014, Publication 525 says Form 1099-B basis will not reflect amounts included in income upon grant or exercise, and after a disqualifying disposition basis is the exercise price plus the amount reported as wages — so the fix belongs on Form 8949. Skip it and the client is taxed on the same spread twice — as wages and as capital gain. Our post on wash sales and tax-loss harvesting covers other Form 8949 adjustments, and our Form W-2c guide helps when code V or disqualifying-disposition wages are missing.

ISO vs NQSO review checklist

• Read the grant agreement to confirm ISO or NQSO status.
• Tie every Form 3921 to a Form 6251 adjustment or a same-year sale.
• Track grant and exercise dates per lot to test both holding periods.
• Check W-2 box 12 code V for NQSO exercises and box 1 for disqualifying dispositions.
• Adjust 1099-B basis on Form 8949; keep separate regular and AMT basis.
• Flag founders and early employees for related planning such as the §1202 QSBS exclusion.

On the employer side, Haynes Boone cautions that if employees won’t exercise until an exit, they will never realize the favorable ISO treatment, and it would be simpler to grant NQSOs.

Where Tax Brew fits

Equity compensation returns are documentation-heavy. Tax Brew provides bookkeeping, cleanup and tax prep support for US CPA firms, including lot-level basis schedules and workpapers that tie Forms 3921, W-2 and 1099-B to the return, with the first 20 hours free for qualifying engagements. Your team keeps the advice and the sign-off. See our services, or email info@taxbrewglobal.com.

Sources: Haynes Boone, “Refresher on Incentive Stock Options” (Oct. 5, 2026); IRS Topic 427, Stock options (last reviewed Sept. 24, 2026); IRS Publication 525 (2025); Instructions for Forms 3921 and 3922 (Rev. April 2025); 26 U.S.C. §421, §422, §83 and §56(b)(3) (Cornell LII). General information, not tax or legal advice.