Last Updated: April 2026
The choice between RSUs, Non-Qualified Stock Options (NSOs), and Incentive Stock Options (ISOs) is one of the most consequential tax decisions an employee can face — yet most employees never actually choose: their company chooses for them. Large public tech companies predominantly grant RSUs. Early-stage startups predominantly grant ISOs. And the tax outcomes differ dramatically. This guide builds the complete tax comparison at 2026 rates — including the often-overlooked Alternative Minimum Tax exposure for ISO exercises and the Section 1202 QSBS exclusion opportunity that can make startup ISOs extraordinarily valuable on an after-tax basis. For an interactive estimate of RSU taxes specifically, use the RSU Tax Calculator.
The table below models three employees at the same company, each receiving $100,000 in grant-date value: one as RSUs (1,000 RSUs at $100/share), one as NSOs (2,000 options, strike $50, FMV at grant $100 = $50 spread each = $100K grant value), and one as ISOs (same as NSOs). Assumptions: $150,000 base salary, single filer, 2026 IRS brackets. Scenario A: shares sold immediately at vest/exercise. Scenario B: shares held 12+ months post-vest/exercise then sold at $150 (50% appreciation).
| Type | Ordinary Income Event | Ordinary Income Tax | Capital Gain on Sale (Scenario B) | Total Tax (Scenario B) |
|---|---|---|---|---|
| RSU | Vest: $100K at ordinary income (24% bracket) | ~$24,000 federal + FICA | $50K gain × 15% LTCG = $7,500 | ~$31,500 |
| NSO | Exercise: $100K spread at ordinary income (24%) | ~$24,000 federal + FICA | $50K gain × 15% LTCG = $7,500 | ~$31,500 |
| ISO (qualifying) | No ordinary income (regular tax) — AMT may apply | $0 regular OI tax (possible AMT — see below) | $150K total gain × 15% LTCG = $22,500 | ~$22,500 |
ISO scenario assumes no AMT, qualifying disposition (held 2+ years from grant, 1+ year from exercise), and no disqualifying disposition. FICA does not apply to ISO exercises. Note: state income tax applies on top of all scenarios — California provides no LTCG preference, so CA residents owe CA ordinary income rates on all three scenarios.
The ISO advantage in Scenario B is significant: ~$9,000 in tax savings ($31,500 vs $22,500) on the same economic outcome. But this comes with two major conditions: (1) you must hold the shares for the qualifying periods without selling, exposing you to stock price risk; and (2) the ISO exercise spread may trigger AMT in the exercise year.
The AMT is the primary risk of ISO exercises. Here is how to model it before exercising.
Example: Employee exercises 2,000 ISOs with a $50 strike price when the stock is trading at $150. Spread = $100/share × 2,000 shares = $200,000 AMT preference item. Base salary: $150,000. Regular taxable income (after standard deduction): $133,900. Regular federal tax on $133,900: approximately $24,734. AMTI calculation: $133,900 + $200,000 (ISO spread) = $333,900. Minus AMT exemption ($137,000) = $196,900. AMT at 26% = $51,194. Regular tax = $24,734. AMT owed = $51,194 − $24,734 = $26,460 of additional AMT in the exercise year.
The AMT credit saves you later: The $26,460 AMT paid generates an equal AMT credit (Form 8801) that can be used in future years when your regular tax exceeds your AMT. So the AMT is often a timing cost rather than a permanent cost. However, if the stock price falls significantly between exercise and the AMT-due date, you may owe AMT on gains that no longer exist.
Planning tool — the AMT crossover: There is a maximum ISO spread you can exercise in a given year without triggering AMT. This is the amount that, when added to regular AMTI, still leaves regular tax above the AMT. For a $150K salary single filer in 2026, this is approximately $130,000 in ISO spread (rough estimate — model your exact situation). Spreading ISO exercises over multiple years can stay below the AMT crossover each year, converting the full gain to LTCG without AMT cost.
For startup employees who hold ISOs and qualify for Qualified Small Business Stock (QSBS) treatment under IRC Section 1202, the after-tax economics become extraordinary.
What QSBS provides: Up to $10,000,000 in capital gains (or 10× the investor's basis, whichever is greater) from the sale of QSBS can be excluded from federal capital gains tax entirely (100% exclusion for shares acquired after September 27, 2010). This federal exclusion also eliminates the 3.8% Net Investment Income Tax on the excluded amount.
QSBS qualification requirements: The company must be a C-corporation with gross assets under $50 million at the time of stock issuance. The stock must be acquired at original issuance (not purchased from another shareholder). The employee must hold the shares for more than 5 years. The company must be an active business in a qualifying industry (technology, life sciences, retail, professional services — but not hospitality, finance, law, or health).
ISO + QSBS interaction: If an employee exercises ISOs in a qualifying company, holds the shares for 5+ years, and meets all QSBS requirements, up to $10M of the resulting gain may be entirely federal-tax-free. The ISO holding period (2 years from grant, 1 year from exercise for LTCG) must also be met — most long-term startup employees naturally satisfy both holding periods simultaneously.
State treatment: California does not conform to the federal QSBS exclusion. California taxes the entire gain as ordinary income regardless of Section 1202. New York also does not conform. The QSBS benefit is federal only for residents of non-conforming states.
RSUs cannot qualify for QSBS: QSBS requires stock issued at original issuance. RSUs are settled in stock at vest — the company issues new shares. Whether RSU-settled shares qualify for QSBS is a contested legal question; the prevailing view is that they do not qualify, because there is no stock issued at the time of the original grant. ISOs, when exercised, result in stock purchased at original issuance — they are the primary QSBS-eligible equity vehicle for employees.
Prefer RSUs when: You work at a public company where stock has an established price; you do not want investment risk on unvested equity; you prefer simplicity; your marginal rate is below 24% (the withholding gap is small); or you plan to donate shares to a DAF to eliminate post-vest capital gains in a high-tax state.
Prefer ISOs when: You are at an early-stage startup where the FMV is low relative to the potential exit value; the AMT crossover is manageable given your salary level; you can hold shares for 5+ years for potential QSBS treatment; and the company is likely to grow significantly before any liquidity event.
Prefer NSOs when: ISOs are limited by the $100K cap and you have been granted additional options above that cap (which automatically become NSOs); or you exercise NSOs in a year when the spread is small or the stock price is near the strike (minimising the ordinary income event).
The early startup ISO exercise strategy: Exercise ISOs early in a startup's life when FMV is low and close to the strike price. The spread is minimal, so AMT exposure is minimal. You start the 5-year QSBS clock and the 1-year capital gains holding period immediately. If the company succeeds, the entire appreciation from the low exercise-date FMV to sale is LTCG or QSBS-excluded. The risk: if the company fails or the stock falls below your exercise price, you lose the exercise cash and have a capital loss (which is limited in deductibility). An 83(b) election is required within 30 days of exercise to lock in the low FMV as ordinary income for restricted stock — though ISOs exercised early use a different mechanism, consult a specialist before early exercise.
CountryTaxCalc.com is reader-supported. When you use our partner links, we may earn a commission at no cost to you. Learn more about our affiliate partnerships
★ 4.8 Trustpilot · 1,625 reviews
Greenback specialises in US tax returns including RSU vesting, stock option exercises, ISO/NSO treatment, and AMT calculations. Flat-fee pricing with IRS-enrolled agents.
⚠ Not the cheapest option — best for complex situations and expats who want a dedicated CPA.
Get Expert Help with Equity Compensation Taxes →★ 4.7 Trustpilot · 8,728 reviews
Deel helps companies grant RSUs, options, and other equity to employees across 150+ countries — handling local tax withholding, reporting, and compliance automatically.
⚠ For employers and companies only — not for individual freelancers or employees.
Manage Global Equity Compensation with Deel →RSUs create a tax event at vest — the full FMV at vest is ordinary income, taxed immediately with no choice or timing flexibility. Stock options (NSOs and ISOs) create the primary tax event at exercise, which you control within the exercise window. NSOs are taxed as ordinary income on the spread at exercise. ISOs may qualify for long-term capital gains treatment if you hold the shares long enough and avoid the AMT. RSUs are simpler; options offer more tax planning opportunity at the cost of complexity and risk.
For NSOs: yes, the spread at exercise is subject to FICA (Social Security up to the $184,500 wage base in 2026, Medicare 1.45% uncapped, plus AAMIT above $200,000 single). For ISOs: no FICA on exercise if the qualifying holding periods are met. This is one of the ISO advantages that is often overlooked — a large ISO exercise can avoid both ordinary income tax and FICA, whereas the same economic value delivered as RSUs would have been subject to both.
A disqualifying disposition occurs when you sell ISO shares before meeting both holding period requirements: 2 years from the grant date AND 1 year from the exercise date. If you sell early, the ISO loses its preferential tax treatment. The gain up to the spread at exercise becomes ordinary income (as if it were an NSO), and any additional appreciation is a short-term capital gain. The AMT paid at exercise may generate a credit but the ordinary income at sale will be high. Disqualifying dispositions are common when employees need liquidity or when a company is acquired shortly after exercise.
At large public companies, equity type is typically standardised — most grant RSUs with no option for employees to choose. At startups and earlier-stage companies, there is sometimes flexibility, particularly for senior hires. If you are negotiating a startup offer, requesting ISOs over NSOs (within the $100K annual vesting limit) is worth asking for, as ISOs offer better tax treatment at no cost to the company. Above the $100K cap, options must be NSOs regardless of what they are called.
Partially. California conforms to the ISO ordinary income exclusion at exercise (no CA ordinary income tax at ISO exercise, consistent with federal). However, California taxes all capital gains as ordinary income — there is no LTCG preference in California. So the federal benefit of converting ISO gains to 0%/15% LTCG does not reduce California tax. A California resident who holds ISO shares qualifying for 15% federal LTCG still pays 9.3%–13.3% California tax on the same gain as ordinary income. Additionally, California does not conform to the federal QSBS exclusion.
IRC Section 422 limits the amount of ISOs that can vest in a single calendar year to $100,000 in aggregate FMV (valued at the grant date). Options scheduled to vest above this limit in any year are automatically treated as NSOs, even if the grant documentation calls them ISOs. For fast-growing companies where stock value increases significantly after grant, later vesting tranches that were below the $100K cap at grant date may have a market value well above $100K at vest — the cap is calculated at grant date FMV, not vest date FMV.
The RSU Tax Calculator is designed specifically for RSU vests — it calculates federal and state income tax plus FICA on the vest-date FMV as ordinary income. For NSOs, the same calculation applies: enter the spread value (FMV minus strike price, times number of options exercised) as the vest/grant value. For ISOs, the calculator is not directly applicable because ISO exercises do not generate ordinary income at exercise under regular tax — you would need to model the AMT separately. The calculator is most accurate for RSUs and NSOs.
In an acquisition, your equity treatment depends on the deal terms and your grant agreement. Common outcomes: vested options may be cashed out at the acquisition price minus strike (generating ordinary income for NSOs); unvested options may be accelerated (if you have a double-trigger or single-trigger acceleration clause), exchanged for acquirer options, or cancelled with a cash payout. ISOs cashed out in an acquisition may lose their ISO character and be treated as NSOs in certain scenarios. Review your option agreement's change-of-control provisions carefully when an acquisition is announced — the 90-day post-termination exercise window may be shortened or the options may expire at closing.