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RSU vs ISO vs NSO - what's the difference?

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Short answer: RSUs (Restricted Stock Units) are shares granted that vest over time and are taxed as ordinary income at vesting. ISOs (Incentive Stock Options) are options to buy shares at a fixed price, with favorable tax treatment if held long enough but subject to Alternative Minimum Tax (AMT). NSOs (Non-Qualified Stock Options) are options with no special tax treatment and ordinary income tax on exercise. Most public companies use RSUs; most private startups use ISOs or NSOs.

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The three forms compared

Feature RSU ISO NSO
What you get Shares granted at vesting Right to buy shares at fixed price Right to buy shares at fixed price
Cost to exercise None Strike price Strike price
Tax at grant None None None
Tax at vesting/exercise Ordinary income on FMV at vesting AMT may apply at exercise Ordinary income on spread
Tax at sale Capital gain on appreciation since vest Capital gain (LTCG if holding requirements met) Capital gain on appreciation since exercise
Holding requirement for preferential tax None 1 year from exercise + 2 years from grant None
Maximum annual grant None $100K of grant date FMV None
Who can receive Anyone Employees only Anyone (employees, contractors, advisors)
Common at Public companies, late-stage private Early-stage private Mid-late stage private, certain executives

RSUs in detail

A Restricted Stock Unit is a promise to deliver a share of stock at a future date (the vest date). Unlike options, you pay nothing for the share at vesting; you just receive it.

Tax mechanics:

Because RSUs trigger ordinary income at vesting, public companies typically withhold shares to cover the tax liability ("sell-to-cover" or "net settlement"). You receive only the net shares after tax withholding.

Common at: Public companies (because the liquidity to pay vesting taxes exists), late-stage private companies (because RSU vesting can be deferred until liquidity events).

Negotiation considerations:

ISOs in detail

An Incentive Stock Option is a right to buy a share at a fixed price (the strike price or exercise price), with preferential tax treatment if specific holding requirements are met.

Tax mechanics:

Holding requirements for qualifying disposition:

Common at: Early-stage private companies. The maximum annual grant is $100K of grant date FMV per employee (any excess is treated as NSO).

The 90-day exercise window problem:

When you leave the company, ISOs must be exercised within 90 days of termination to retain ISO status. After 90 days, they convert to NSOs (taxed as ordinary income at exercise on the spread). For employees with significant ISO holdings at private companies, this 90-day deadline can force expensive tax decisions.

Negotiating an extended post-termination exercise period (3-10 years) preserves ISO value and avoids the forced conversion. See How to negotiate a job offer for context.

AMT exposure:

The AMT effect of ISO exercise can create large tax bills in the year of exercise, especially for high-spread exercises. Some employees plan ISO exercises across multiple tax years to manage AMT exposure. Consult a tax advisor before exercising large ISO positions.

NSOs in detail

A Non-Qualified Stock Option is a right to buy a share at a fixed price with no special tax treatment.

Tax mechanics:

Common at: Mid-late stage private companies, executives whose ISO grants would exceed the $100K annual limit, contractors and advisors (who cannot receive ISOs).

No holding requirement for preferential tax, but capital gains rates do apply on post-exercise appreciation if held long enough (1 year for long-term capital gain).

Typical practical use: NSOs are simpler than ISOs (no AMT complexity, no holding requirements, no $100K limit). They're often used when ISOs are not practical due to the ISO limit, when the grantee is not an employee, or when companies want simpler tax outcomes.

Practical implications for negotiation

When evaluating an equity offer, look at:

Form of equity: RSU, ISO, NSO. Each has different tax dynamics. Make sure you understand which form you're being offered.

Strike price (for options): For ISOs and NSOs, the strike price is the exercise price you'll pay. Lower strike = better. Companies are required to set strike at no less than fair market value at grant, but the "fair market value" determination matters.

409A valuation: For private companies, the 409A valuation determines option strike prices. A recent low 409A means lower strike prices for new option grants.

Vesting schedule: Standard is 4 years with 1-year cliff. Some startups offer accelerated schedules; some plans have monthly vesting after cliff.

Post-termination exercise window: Default 90 days for ISOs. Negotiate extension to 3-10 years to preserve flexibility.

Treatment in M&A: Double-trigger acceleration applies to all forms. Make sure your acceleration language covers your specific equity type.

Reporting requirements: ISO exercises require specific tax reporting. RSU vesting is reported on your W-2. NSO exercises produce a Form 1099-NEC or W-2 reporting.

Liquidity: For private company equity, when can you actually sell? Some companies have ROFR restrictions, tender offers, or other liquidity structures.

What to do next

If you want a delivered analysis of your specific equity offer, including tax implications, market benchmarks, and recommended language to ask for, we deliver one in 24 hours for $199. See Offer Review.

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Last updated: Sun May 31 2026 00:00:00 GMT+0000 (Coordinated Universal Time)

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