What Is the Difference Between ISOs and NSOs?
Incentive stock options (ISOs) and non-qualified stock options (NSOs) are the two types of stock options a startup can grant.
Every stock option grant at a private company is either an ISO or an NSO, and which one you have affects who was allowed to receive it, how much you’ll owe in tax, and when. The difference comes down to a set of IRS rules under Section 422 of the tax code. Meet them, and you get ISO treatment; don’t, and the grant is automatically an NSO. This post covers what each one is, how the tax treatment differs at exercise and at sale, and how to check which type you actually have.
What is an ISO?
An incentive stock option (ISO) is a type of stock option that can qualify for favorable tax treatment, potentially long-term capital gains rates on the entire gain, rather than ordinary income tax. ISOs can only be granted to employees, not contractors, consultants, or outside board members, and are subject to a $100,000 annual limit (explained below) and other technical requirements under Section 422 of the Internal Revenue Code.
What is an NSO?
A non-qualified stock option (NSO), sometimes called a non-statutory stock option, is the default type of option. Anyone can receive one, including employees, contractors, advisors, and board members, and there’s no special IRS-mandated tax treatment attached to it. The tradeoff for that flexibility is tax simplicity working against you: the spread between your strike price and fair market value is taxed as ordinary income at the time you exercise, regardless of how long you hold the shares afterward.
What’s different about how they’re taxed at exercise?
Exercising an NSO creates an immediate ordinary income tax event — the spread between your strike price and current fair market value gets added to your taxable income for the year, subject to your regular income tax rate and, in many cases, payroll tax withholding. Exercising an ISO doesn’t create ordinary income tax at exercise, but it can trigger the alternative minimum tax (AMT), a parallel tax system that treats that same spread as a preference item, meaning you may still owe real tax at exercise even without a formal “ordinary income” charge.
What’s different about how they’re taxed at sale?
For an NSO, there’s nothing special left to happen at sale beyond standard capital gains treatment: you’ve already paid ordinary income tax on the spread at exercise, so any further gain or loss between your exercise-date value and your eventual sale price is taxed as a short- or long-term capital gain, based on how long you held the shares after exercising. For an ISO, the outcome depends on whether you meet the holding period for what’s called a “qualifying disposition,” selling only after holding the shares for at least one year from exercise and two years from the original grant date. Meet both, and the entire gain from your strike price to the sale price is taxed at long-term capital gains rates. Miss either deadline, a “disqualifying disposition,” and the spread at exercise gets taxed as ordinary income after the fact, largely erasing the ISO’s advantage over an NSO.
Who can receive each type?
Only employees can receive ISOs. Not contractors, consultants, or non-employee board members, who can only be granted NSOs regardless of how core their work is to the company. Employees can receive either type, and many do end up holding both if their company has issued option grants across different periods or under different plans.
What is the $100,000 ISO limit?
The IRS limits how much ISO value can become exercisable for the first time in any single calendar year: only the first $100,000 worth of ISOs (measured using the fair market value at grant, not the strike price) that first become exercisable in a given year actually get ISO treatment. Anything vesting beyond that $100,000 threshold in the same year is automatically treated as an NSO instead, even though it came from the same grant and the same option plan. This mostly affects employees with large grants or accelerated vesting, since it takes a sizable annual vesting tranche to cross the threshold.
Worked example
Say you have 10,000 options with a $2 strike price, and you exercise when fair market value is $12 a share, a $10-per-share spread, or $100,000 total.
If these are NSOs: the full $100,000 spread is taxed as ordinary income in the year you exercise. At a 32% marginal rate, that’s roughly $32,000 in tax due at exercise, regardless of what you do with the shares afterward.
If these are ISOs, and you hold for a qualifying disposition: at exercise, the $100,000 spread is an AMT preference item. For a single filer with no other AMT income, using the 2026 exemption of $90,100, that’s roughly $2,600 in AMT due at exercise. Far less than the NSO scenario. If you later sell after meeting both ISO holding requirements, the full gain is taxed at long-term capital gains rates (commonly 15–20%) instead of ordinary income rates, which can mean a meaningfully smaller total tax bill than the NSO path, in exchange for tying up your capital longer and taking on the company-specific risk of holding shares that long.
These are simplified, illustrative numbers. Your actual tax outcome depends on your full income picture, state taxes, and how the AMT credit interacts with your regular tax in future years, so it’s worth running your specific numbers with a tax professional.
FAQ
Can I have both ISOs and NSOs at the same company? Yes. It’s common for a single employee to hold both, especially if grants were issued across different vesting periods or if the $100,000 annual limit converted part of a large grant into NSOs.
What is a disqualifying disposition? Selling ISO shares before meeting both holding requirements, one year from exercise and two years from grant, which causes the spread to be taxed as ordinary income instead of getting long-term capital gains treatment.
Does converting from ISO to NSO happen automatically? Yes, in two situations: when vesting in a calendar year exceeds the $100,000 ISO limit, and when ISO shares are sold in a disqualifying disposition. Both happen automatically under IRS rules, with no separate paperwork required from you.
Do contractors or advisors ever get ISOs? No. ISOs are legally restricted to employees. Contractors, consultants, and non-employee board members can only receive NSOs.
Which is better, ISOs or NSOs? Neither is universally better. ISOs offer the possibility of lower long-term tax if you meet the holding requirements, but come with AMT exposure and more complexity; NSOs are simpler and more predictable but tax the full spread as ordinary income right away. The type you have is generally set by your role and your company’s option plan, not something you choose.
What to do next
Your option grant agreement or your company’s equity plan administrator will show which type you hold. Don’t assume based on general averages. You can model your own exercise costs and estimated tax impact for either type at movewealth.io.
MoveWealth is not a broker-dealer, investment adviser, or lender. This is educational content, not financial, tax, or legal advice. Consult a qualified professional about your specific situation.