Stock options come in two types with very different tax treatment. NSOs (Non-Qualified Stock Options): spread at exercise is ordinary income, taxed at up to 37% federal + state rates. ISOs (Incentive Stock Options): no regular income tax at exercise, but the spread is an AMT (Alternative Minimum Tax) preference item — the 'ISO AMT trap.' Long-term capital gains treatment applies if you hold ISO shares 1 year after exercise AND 2 years after grant date. State tax treatment varies — California follows the federal regular-tax treatment of ISOs but applies its own alternative minimum tax to the exercise spread.
At a glance
Key Facts
NSO Federal Tax
Spread at exercise (FMV minus strike price) is ordinary income; taxed at up to 37% federal + state; employer withholds FICA + income tax
ISO Federal Regular Tax
No ordinary income at exercise for regular income tax purposes; spread is AMT preference item — may trigger AMT at 26–28% on the spread
ISO Holding Period
To get long-term capital gains on ISOs: hold shares 1 year after exercise AND 2 years after grant date; otherwise sale is a 'disqualifying disposition' taxed as ordinary income
California ISO Treatment
California follows the federal rule that an ISO exercise is not a regular-tax event, but its own alternative minimum tax counts the exercise spread; a disqualifying disposition is ordinary income
AMT Threshold (2026)
AMT exemption: $90,100 (single) / $140,200 (married filing jointly); AMT rate 26% on AMTI up to $244,500; 28% above. ISO exercises increase AMTI.
83(b) Election
For options exercised on restricted/unvested shares: filing an 83(b) election within 30 days of exercise locks in value for tax purposes at exercise, potentially saving significant ordinary income tax if shares appreciate
Introduction
Stock options are a primary component of startup and tech company compensation. The federal tax treatment of ISOs vs NSOs is well-documented, but the state income tax dimension — particularly California's aggressive ISO treatment and the complex multi-state rules when employees move during option vesting — is critical and often misunderstood.
Section 01
NSO vs ISO: Federal Tax Treatment
Understanding the two option types is essential:
Non-Qualified Stock Options (NSOs)
NSOs are the simpler type for tax purposes:
At exercise: The spread (FMV at exercise minus strike price) is ordinary income, included on your W-2 (employee options) or 1099-NEC (contractor options). FICA applies to W-2 NSO income. State income tax applies at your state rate.
After exercise: If you hold the shares, appreciation above the exercise FMV is taxed as capital gains (short-term or long-term depending on hold period from exercise date).
Incentive Stock Options (ISOs)
ISOs have preferential regular income tax treatment but AMT complexity:
At grant: No tax event.
At exercise: No regular income tax (the spread is NOT ordinary income for regular tax purposes). However, the spread is an AMT preference item — it increases your Alternative Minimum Income (AMTI), potentially triggering AMT.
At sale: If you satisfy holding periods (1 year from exercise + 2 years from grant), the entire gain from strike price to sale price is taxed as long-term capital gains (0%, 15%, or 20% federal). If you sell before holding periods (disqualifying disposition), the spread at exercise becomes ordinary income.
The ISO AMT Trap
The most dangerous scenario: exercising a large ISO grant in a year when the stock is highly valued. The spread (FMV at exercise minus strike price) is included in AMTI. If AMTI exceeds the exemption, you owe AMT — potentially a six-figure bill — while holding stock that may subsequently decline. Classic case: tech employee exercises ISOs in a banner year, stock falls 70% the following year, tax bill remains. The 2022 tech correction created this scenario for many employees. AMT paid creates an AMT credit that can be recovered in future years when regular tax exceeds AMT — but recovery takes years and the stock may never recover.
Section 02
California's ISO Treatment and Multi-State Allocation
California is the most important state for stock option taxation because of its large share of startup equity and its nonresident sourcing rules:
California ISO Exercise: AMT, Not Regular Tax
California follows the federal rule that exercising an ISO is not a regular income tax event. California’s own alternative minimum tax, however, counts the exercise spread as income in the year of exercise, so an ISO exercise can trigger California AMT even when no regular California tax is due. A disqualifying disposition (selling before the holding periods are met) is ordinary income for California, as it is federally. By contrast, the spread on an NSO is ordinary income at exercise for California income tax (top rate 13.3%).
Multi-State Allocation for Stock Options
Like RSUs, stock options with multi-year vesting are allocated across states based on workdays in each state during the vesting period:
California allocates option income (NSO spread or ISO spread) based on CA workdays / total workdays during the period from grant to exercise (or grant to vest for restricted options)
Moving from California to Texas before exercising options does not eliminate California's claim — CA will allocate a portion based on the CA workdays during vesting
New York applies similar sourcing rules
83(b) Election for Early Exercise
Many startup employees are given the option to early-exercise unvested NSOs (before vesting). If you early-exercise and file an 83(b) election within 30 days: you recognize ordinary income today based on the current spread (often near zero for startup options at exercise price ~FMV). Future appreciation is capital gains. Without an 83(b) election, each vesting event creates an ordinary income recognition event at the then-current spread — potentially at much higher value if the startup has appreciated. The 83(b) is one of the most valuable elections for early-stage startup employees and founders.
ISO AMT planning, NSO exercise timing, 83(b) elections, and multi-state option allocation require expert guidance. TaxHub connects you with CPAs who specialise in startup and tech equity compensation.
⚠ Not for simple single-state returns. Free filing is fine for straightforward W-2 situations.
US expats with stock options face complex multi-jurisdiction issues: source country taxation, US reporting, and treaty interaction. Greenback specialises in US expat equity compensation tax.
⚠ Not the cheapest option — best for complex situations and expats who want a dedicated CPA.
The ISO AMT trap: when you exercise ISOs with a large spread, the spread is added to your Alternative Minimum Income (AMTI). If AMTI significantly exceeds the AMT exemption ($90,100 single in 2026), you owe AMT at 26–28% on the spread — even though you haven't sold the shares and may have no cash to pay the tax. To avoid the trap: (1) Exercise ISOs incrementally across multiple years to stay below the AMT phaseout; (2) Model your AMT exposure before exercising (use Form 6251 calculations or consult a CPA); (3) Exercise in years when your regular income is low (to maximize the regular tax vs AMT spread); (4) Consider NSO vs ISO trade-offs if your company offers a choice. If you're already in the trap, the AMT credit on Form 8801 recovers AMT paid in future years when regular tax exceeds AMT.
Q
If I move from California to Texas before exercising my ISOs, do I owe California tax?
Possibly. California taxes nonresidents on California-source income, and the FTB sources an NSO spread (or the ordinary income from an ISO disqualifying disposition) by California workdays over the period from grant to vest. Exercising an ISO is not a regular-tax event for California, although California AMT can apply. Example for an NSO: options were granted 4 years ago in California and you moved to Texas 2 years ago, so 2 of the 4 vesting years were worked in California and about 50% of the spread is California-source. You report it as a nonresident (Form 540NR). The longer the vesting period you spent in California, the higher your California allocation. Executing a genuine California departure well before exercise — and maximizing the non-CA vesting period — reduces the CA allocation.
Q
What is an 83(b) election and when should I file it?
An 83(b) election allows you to recognize income on restricted property (including unvested shares from early-exercised options) at the current value — rather than waiting for vesting events. You must file within 30 days of receiving the property (early exercise date). The benefit: if your options are at strike price near FMV at grant, the spread is near zero — you recognize near-zero income now. All future appreciation is capital gains (long-term if held 12+ months from exercise). Without 83(b), each vest event creates ordinary income recognition at the then-current value. For startup employees receiving early-exercise options, the 83(b) can save dramatically on taxes if the company succeeds. The risk: if the company fails and you forfeited the shares, you cannot recover the tax already paid.
Disclaimer:This guide provides general tax information for educational purposes only. Stock option taxation (ISO, NSO, AMT, 83(b)) is highly complex and fact-specific. This is not tax or legal advice. Consult a CPA or tax attorney for your specific equity compensation situation.