Nonqualified Stock Options (NSOs): A Tax Guide

What is an NSO?

A Nonqualified Stock Option (NSO) is a form of equity compensation that gives you the right to purchase company stock at a fixed price — the strike price — typically set at the fair market value (FMV) on the grant date. The “nonqualified” label means the option doesn’t meet the requirements of Section 422 of the Internal Revenue Code, which is what defines Incentive Stock Options (ISOs). NSOs don’t get the favorable AMT-only tax treatment that ISOs do — but they’re more flexible in other ways, which is why later-stage and public companies often grant them instead.

NSOs also appear at earlier-stage companies in two specific places: as the “overflow” when an ISO grant exceeds the $100K annual exercisability limit (the excess is automatically reclassified as NSOs), and as the only kind of option a company can grant to non-employees like contractors, advisors, and board members.

Who Gets NSOs (and Why Companies Grant Them)

Eligibility for NSOs is much broader than for ISOs:

• Employees, just like ISOs.
• Non-employees: independent contractors, advisors, board members, consultants. ISOs are restricted to employees by statute; NSOs have no such restriction.

From the company’s perspective, NSOs offer some advantages over ISOs:

• No $100K cap. A company can grant arbitrarily large NSO packages to a single employee.
• No employee-only restriction. Non-employees can be compensated with NSOs.
• The company gets a tax deduction at exercise equal to the bargain element the employee recognizes as ordinary income. ISOs give the company no deduction unless the employee makes a disqualifying disposition.

That last point is meaningful: from a corporate-tax-planning perspective, NSOs effectively shift the tax bill to the employee while giving the company a matching deduction. ISOs sit purely on the employee side.

The Tax Timeline: Three Key Moments

Three moments matter for NSOs:

1. Grant

Typically no tax at grant, assuming the strike price equals or exceeds FMV on the grant date. (If the strike is set below FMV, you’ve stumbled into Section 409A territory — see the note at the end.)

2. Vesting

No tax at vesting. You haven’t exercised yet — you just have the legal right to do so.

3. Exercise

This is where NSOs and ISOs sharply diverge.

When you exercise an NSO, the bargain element — the difference between the FMV on the exercise date and the strike price — is ordinary income, recognized in the year you exercise. For employees, it flows onto your W-2 Box 1 (and Boxes 3 and 5 for FICA purposes). For non-employees, it appears on a 1099 and may be subject to self-employment tax depending on your situation.

Crucially, the bargain element is also subject to FICA, Medicare, and the 0.9% Additional Medicare Tax — unlike ISOs, where the bargain element flows only through AMT and avoids payroll taxes entirely.

After exercise, your cost basis in the shares is the FMV at exercise — not the strike price. This is the critical fact that drives the cost-basis trap below.

4. Sale

When you eventually sell the shares, the gain or loss is the difference between the sale price and your cost basis (FMV at exercise). It’s a long-term capital gain if you’ve held the shares more than a year from exercise, otherwise short-term.

The Net Investment Income Tax (NIIT) of 3.8% may apply if your modified adjusted gross income exceeds the threshold for your filing status.

Withholding at Exercise

Because the bargain element is ordinary income (and FICA wages), your employer is required to withhold federal income tax, state income tax (where applicable), Social Security, and Medicare at the time of exercise. This is generally handled in one of two ways:

• Cashless exercise / sell-to-cover. Your broker simultaneously exercises the options and sells enough of the resulting shares to cover the strike price and the withholding. You receive the net shares.
• Cash exercise. You write a check (or have funds withdrawn from your account) for the strike price plus the withholding. You receive all the shares.

The withholding rate on the bargain element is typically the federal supplemental wage withholding rate of 22% (or 37% above $1 million). For high earners whose actual marginal rate is 32%, 35%, or 37%, this can leave you significantly under-withheld. The shortfall plus any state-tax shortfall hits you at filing time — same trap covered in the RSU guide.

If your bargain element is large, this also has estimated tax payment implications: the IRS expects withholding to track your liability throughout the year, and a large NSO exercise can trigger an underpayment penalty if not planned for.

The Cost-Basis Trap

This is the single most expensive filing mistake on NSO sales, and it’s overwhelmingly common.

When you sell shares acquired from an NSO exercise, your broker issues a 1099-B reporting the sale. The cost basis your broker reports is often just the strike price you paid — not the FMV at exercise that includes the bargain element you’ve already paid ordinary income tax on.

Example. You exercise NSOs at a $10 strike when FMV is $50. You pay ordinary income tax on the $40 bargain element via your W-2. Your basis in the shares is $50 (strike + bargain element). A year later, you sell at $60.

• Correct treatment: capital gain = $60 − $50 = $10. Tax on $10 of LTCG.
• What the broker may report on 1099-B: cost basis = $10 (just the strike). Capital gain = $60 − $10 = $50.

If you don’t catch this and adjust the basis on Form 8949, you’ll pay capital gains tax on $50 — even though $40 of that is the bargain element you already paid ordinary income tax on. You’ve been double-taxed on the same income.

The fix: when you file, manually adjust the cost basis on Form 8949 (column (g), with adjustment code “B”) to reflect the true basis. Most tax software will prompt for this when it sees an NSO sale, but only if you correctly identify the shares as NSO-acquired. Always cross-check that your reported basis equals FMV at exercise — not just the strike.

NSOs vs ISOs at a Glance

	NSOs	ISOs
Eligible recipients	Employees + non-employees	Employees only
Annual cap	None	$100K of grant-date FMV becoming exercisable per year
Tax at exercise	Ordinary income on bargain element + FICA	AMT income on bargain element (no FICA)
Holding period for favorable treatment	1 year from exercise (LTCG on appreciation only)	2 years from grant + 1 year from exercise (LTCG on entire gain)
AMT exposure	None from the option itself	Yes, at exercise
Employer deduction	Yes, at exercise	No, unless disqualifying disposition
Typically granted by	Later-stage / public companies; non-employee grants; ISO overflow	Earlier-stage startups

The headline difference: ISOs concentrate the tax cost in AMT (potentially recoverable as a credit later) while NSOs concentrate it in ordinary income (paid in cash now, gone forever).

A Concrete Example

You receive 10,000 NSOs with a $5 strike price. Two years later, you exercise when FMV is $25.

At exercise: - Bargain element: ($25 − $5) × 10,000 = $200,000 - This is ordinary income on your W-2 (Box 1 + Boxes 3/5). - Federal income tax withheld at the 22% supplemental rate: $44,000. (If your actual marginal rate is 35%, you’re under-withheld by ~$26,000.) - FICA + Medicare also withheld on $200,000 (with Additional Medicare Tax kicking in if your total Medicare wages exceed the threshold). - Cost basis in the 10,000 shares: $25 × 10,000 = $250,000.

A year later, you sell at $40: - Sale proceeds: $40 × 10,000 = $400,000. - Capital gain: $400,000 − $250,000 = $150,000, treated as long-term capital gain. - Federal LTCG tax (top bracket): 20% × $150,000 = $30,000, plus 3.8% NIIT if applicable = $5,700. Total: ~$35,700.

The shape of the deal: the original $200K of bargain element was taxed as ordinary income at exercise; the additional $150K of post-exercise appreciation got the more favorable LTCG treatment.

Hold After Exercise, or Sell?

The hold-vs-sell decision is simpler for NSOs than for ISOs, because the painful ordinary-income tax has already been paid at exercise. Holding only changes the treatment of additional appreciation:

• Sell immediately at exercise: your bargain element is ordinary income (already taxed); any tiny gain or loss between the exercise price you paid and the sale price is short-term capital gain or loss. Often near-zero.
• Hold for at least 1 year after exercise: future appreciation qualifies for LTCG rates (15%/20% + possible NIIT) instead of ordinary rates.

The trade-off: holding requires conviction in meaningful appreciation from the exercise-date FMV, plus tolerance for the concentration risk of holding more of your employer’s stock. The bulk of the tax efficiency from NSOs (vs. owning cash) is captured at exercise — the holding decision is a separate question about whether future appreciation will be material enough to make LTCG treatment worthwhile.

A common pattern in practice: some shares get sold immediately to cover the exercise cost and tax shortfall, and the remainder is held for a year or more to qualify for LTCG on any further appreciation.

A Note on Section 409A

If your NSOs are granted with a strike price below FMV on the grant date, you fall into Section 409A territory — the IRS treats discount stock options as deferred compensation and imposes a 20% additional tax plus interest on the recipient (you, not the employer) at vesting. This is in addition to all the regular tax owed on the bargain element.

For private companies, the way employers avoid 409A trouble is by obtaining a 409A valuation — an independent appraisal that establishes FMV — at least every 12 months and after any material event. As an employee, your defense against 409A risk is essentially “make sure your company has a current 409A valuation, and the strike price on your grant equals or exceeds the resulting FMV.” Most reputable employers handle this carefully; if you’re ever offered “discount” options, take a hard look before accepting.

The Takeaway

NSOs are taxed as ordinary income on the bargain element at exercise — full stop, no AMT detour. That triggers federal income tax, FICA, Medicare, and possibly the Additional Medicare Tax in the year of exercise. Cost basis in the resulting shares is FMV at exercise (not the strike), which sets up a common cost-basis trap when 1099-Bs misreport basis as just the strike. Compared to ISOs, NSOs have broader eligibility and no $100K cap but lose the AMT-credit recovery mechanism. The hold-vs-sell decision after exercise is simpler than for ISOs because the painful ordinary income has already been recognized — holding only affects how additional appreciation gets taxed.