Bargain Element: Calculating the Spread on NQSOs and ISOs

The bargain element on stock options is the difference between what you pay to exercise (the strike price) and what the shares are actually worth (the fair market value) on the day you exercise. If your strike price is $10 per share and the stock trades at $50 on exercise day, the bargain element is $40 per share. Multiply that per-share spread by the number of shares exercised, and you have the total bargain element for the transaction. That single number drives nearly every tax consequence that follows.

How to Calculate It

The math is simple. Fair market value per share on the exercise date, minus the strike price, times the number of shares.

Say your grant gives you a strike price of $15 per share and the stock trades at $65 the day you exercise. Your per-share spread is $50. Exercise 400 shares, and the total bargain element is $20,000. That $20,000 is the figure that shows up on tax forms and determines withholding.

The calculation itself never changes. What changes is how the IRS taxes that number, which depends entirely on whether you hold non-qualified stock options (NQSOs) or incentive stock options (ISOs).

Getting the Fair Market Value Right

The strike price is fixed at grant and stays fixed for the life of the option. You’ll find it in your grant agreement or your company’s equity portal.

Fair market value is trickier. For public companies, it’s the closing price on the exchange on the exercise date. For private companies, fair market value comes from an independent appraisal called a 409A valuation, named for the tax code section that requires it. These are generally valid for 12 months or until a significant event occurs, such as a new funding round, an acquisition offer, or a major shift in financial performance. Before exercising private-company options, confirm the 409A is still current. Exercising on a stale valuation creates problems with the IRS later.

NQSOs: Ordinary Income at Exercise

NQSOs trigger tax the moment you exercise. The IRS treats the full bargain element as ordinary compensation income, no different from a paycheck or a bonus. You owe income tax on that amount whether you sell the shares afterward or hold them.

Your employer withholds payroll taxes on the bargain element the same way it does on wages: 6.2% for Social Security (up to the 2026 wage base of $184,500 in combined earnings) and 1.45% for Medicare.¹² If your total earnings for the year exceed $200,000 (single) or $250,000 (married filing jointly), an additional 0.9% Medicare tax applies on the amount above those thresholds.³

For federal income tax, employers withhold at the flat supplemental wage rate of 22%. If your total supplemental wages for the year exceed $1 million, the excess is withheld at 37%.⁴ That 22% flat rate is often not enough. If your marginal rate is 32% or 35%, you’ll owe the difference at filing. Many states withhold on supplemental income too.

Avoiding an Underpayment Penalty

A large exercise can leave you short at tax time even after withholding. The IRS charges a penalty if you haven’t paid enough throughout the year. Under the safe harbor rule, you avoid the penalty if your total withholding and estimated payments cover at least 90% of your current-year tax liability or 100% of last year’s tax (110% if your adjusted gross income exceeded $150,000).⁵ If a big exercise pushes your income well above prior years, run the numbers and make an estimated payment in the quarter of the exercise.

ISOs and the AMT Adjustment

ISOs don’t generate ordinary income tax at exercise. That’s the headline benefit. But the bargain element still counts as an adjustment for the alternative minimum tax, which means you can owe AMT even though your regular return shows no income from the exercise.⁶ The statute strips the favorable ISO treatment for AMT purposes and requires you to recognize the spread as if it were taxable income.⁷

In practice, you calculate tax two ways, once under normal rules and once under AMT rules, and pay whichever is higher. For 2026, the AMT exemption is $90,100 for single filers and $140,200 for married couples filing jointly, with phaseouts beginning at $500,000 and $1,000,000 respectively.⁸ AMT is levied at 26% on the first $244,500 of AMT income above the exemption and 28% above that.

The real hazard is liquidity. You can owe AMT on a bargain element worth hundreds of thousands of dollars while all that value sits locked in stock you haven’t sold. Before exercising a large ISO position, work out whether you can pay the resulting AMT without selling shares.

Recovering AMT Through the Minimum Tax Credit

The ISO bargain element is a “deferral item,” meaning it shifts the timing of income recognition rather than creating a permanent difference. AMT paid on deferral items generates a credit you can use in future years when your regular tax exceeds your AMT. You claim it on Form 8801.⁹ The credit doesn’t expire and carries forward until used. AMT paid on an ISO exercise eventually comes back to you, though the timing depends on your later tax picture.

ISO Holding Periods and Disqualifying Dispositions

To get full ISO tax treatment, hold the shares at least two years after the grant date and at least one year after the exercise date.¹⁰ Meet both, and gain above your strike price qualifies for long-term capital gains rates when you sell.

Sell before either deadline and you trigger a disqualifying disposition. The IRS reclassifies the bargain element (the spread between strike price and fair market value on the exercise date) as ordinary compensation income, just like an NQSO. Your employer reports it on your W-2, and you pay ordinary income tax on that portion. Any additional gain above the exercise-date fair market value is treated as a capital gain.¹⁰

There’s also a ceiling that catches people off guard. If the aggregate fair market value of ISOs becoming exercisable for the first time in any calendar year exceeds $100,000, the excess is treated as non-qualified options.¹⁰ At a fast-growing company, that limit is surprisingly easy to hit.

How the Bargain Element Sets Your Cost Basis

Your cost basis in the shares determines the capital gains tax you owe when you eventually sell. For NQSOs, the cost basis is the strike price plus the bargain element you already reported as income. If your strike price was $15 and the bargain element was $50 per share, your cost basis is $65 per share.¹¹ Sell later at $80, and your capital gain is $15 per share, not $65.

Getting this wrong is one of the most common and expensive mistakes in equity compensation. People report the full sale price minus only the strike price, effectively paying tax on the bargain element twice.

For ISOs that meet the holding period, your cost basis is simply the strike price. The bargain element was never taxed as ordinary income, so it doesn’t get added to basis, and any gain above the strike price at sale is a long-term capital gain. If you triggered a disqualifying disposition, basis follows the NQSO approach: strike price plus whatever portion was reclassified as ordinary income.

Short-term capital gains (shares held one year or less after exercise) are taxed at ordinary income rates, which run from 10% to 37% for 2026. Long-term capital gains top out at 20% for the highest earners. That gap is the entire reason holding-period planning matters.

Funding the Exercise

You have three basic ways to come up with the money to exercise, and each interacts with the bargain element differently.

Cash exercise. You pay the full strike price out of pocket and keep all the shares. Maximum upside, but requires liquid cash and leaves you exposed if the stock drops.
Same-day sale (cashless exercise). You exercise and immediately sell all the shares. The broker uses the sale proceeds to cover the strike price, taxes, and fees, and sends you whatever is left. The bargain element is your entire economic benefit.
Sell-to-cover. You exercise all the options but sell only enough shares to cover the strike price, withholding taxes, and fees. You keep the rest.

For ISOs, both same-day sale and sell-to-cover automatically trigger a disqualifying disposition, since you’re selling before meeting the holding period. If preserving ISO treatment matters, a cash exercise is the only path that keeps the door open.

Section 83(b) Elections for Early Exercise

Some companies, particularly startups, let you exercise options before they vest. Do this, and you receive restricted stock that vests over time. Without action on your part, you don’t owe tax until each batch vests, but the bargain element at each future vesting date could be much larger if the company has grown.

A Section 83(b) election lets you pay tax on the bargain element at the time of the early exercise instead of at each future vesting date. If the stock is still worth close to your strike price when you exercise early, the bargain element is small or zero, meaning little or no tax now, and future appreciation gets taxed as capital gains.¹²

The catch: an absolute 30-day filing deadline. You must file the election with the IRS within 30 days of the exercise date. No extensions, no exceptions. Miss it and you pay ordinary income tax on the spread at each vesting event.

How the Bargain Element Gets Reported

For NQSOs, the bargain element appears on your W-2 in Box 12, identified by Code V, and is included in total wages in Box 1.¹³ Reporting is the employer’s job, but check the numbers against your own records.

For ISOs, your employer furnishes Form 3921, which reports the exercise date, the strike price per share, and the fair market value per share on the exercise date. It’s due to you by January 31 of the year following the exercise.¹⁴ If the exercise triggers AMT, use the Form 3921 data to complete Form 6251, reporting the bargain element as an AMT adjustment on line 2i.⁶

When you sell the shares, your broker issues Form 1099-B. Compare the cost basis on that form against your own. Brokers frequently report NQSO shares with a cost basis equal to just the strike price, leaving out the bargain element already taxed as income. Catch and correct this on your return, or you’ll pay tax on the same income twice.

1
Internal Revenue Service. Topic No. 751, Social Security and Medicare Withholding Rates
2
Social Security Administration. Contribution and Benefit Base
3
Internal Revenue Service. Questions and Answers for the Additional Medicare Tax
4
Internal Revenue Service. Publication 15 (2026), (Circular E), Employer’s Tax Guide
5
Internal Revenue Service. 2026 Form 1040-ES Estimated Tax for Individuals
6
Internal Revenue Service. Instructions for Form 6251 (2025) – Section: Line 2i, Exercise of Incentive Stock Options
7
Office of the Law Revision Counsel. 26 U.S. Code 56 – Adjustments in Computing Alternative Minimum Taxable Income
8
Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026
9
Internal Revenue Service. Instructions for Form 8801 (2025)
10
Office of the Law Revision Counsel. 26 U.S. Code 422 – Incentive Stock Options
11
Internal Revenue Service. Publication 525 (2025), Taxable and Nontaxable Income
12
Office of the Law Revision Counsel. 26 USC 83 – Property Transferred in Connection With Performance of Services
13
Internal Revenue Service. Announcement 2002-108 – Separate Reporting of Nonstatutory Stock Option Income in Box 12 of the Form W-2
14
Internal Revenue Service. Instructions for Forms 3921 and 3922