Learn About Incentive Stock Options

Find out about form 3921 and how employee granted ISO is taxed

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Incentive stock options (ISOs) are a type of employee compensation in the form of stock rather than cash. Your employer grants you an option to purchase stock in the employer's corporation, or parent or subsidiary corporations, at a predetermined price, called the "exercise price" or "strike price."

Stock can be purchased at the strike price as soon as the option vests, becoming available to be exercised. Strike prices are set at the time the options are granted. But the options often vest over time. The ISO allows you to purchase stock in the future at the locked-in strike price if the stock increases in value. This discount on the purchase price of the stock is called the "spread."

Key Takeaways

  • ISOs can be taxed based on their spread, or on any increase or decrease in value.
  • ISO income is exempt from FICA taxes: Medicare and Social Security. But it can be subject to the Alternative Minimum Tax (AMT).
  • ISO income is only included in the AMT income if you hold the stock at the end of the same year in which you exercised the option.
  • ISOs are reported on your Form 1040 tax return in one of three ways, depending on their disposition.

Taxing ISOs

The income from ISOs is subject to regular income tax and alternative minimum tax (AMT). But it's not taxed for Social Security and Medicare purposes.

You'll need the following information to figure out the tax treatment of an ISO:

  • The grant date: The date the ISO was granted.
  • The strike price: The cost to purchase a share of stock.
  • The exercise date: The date on which the option was exercised and shares were purchased.
  • Selling price: The gross amount received from selling the stock.
  • Selling date: The date on which the stock was sold.

How ISOs are taxed depends on how and when you dispose of the stock.

Note

Disposition of stock is when the employee sells the stock. But it can also be transferred to another person or donated to charity.

Qualifying Dispositions of Incentive Stock Options

A qualifying disposition for an ISO means that the stock acquired is disposed of over two years from the grant date and more than one year after the stock was transferred to the employee (often the exercise date). There is an additional qualifying criterion: The taxpayer must have been continuously employed by the employer granting the ISO from the grant date up to three months before the exercise date.

Tax Treatment for Incentive Stock Options

Exercising an ISO is treated as income solely to figure the alternative minimum tax (AMT). But it's ignored when calculating regular federal income tax. The spread between the fair market value of the stock and the option's strike price is considered income for AMT purposes. The fair market value is measured on the day when the stock first becomes transferable or when the employee's right to the stock is no longer subject to the risk of forfeiture.

Note

This inclusion of the ISO spread in AMT income only triggers if the employee continues to hold the stock at the end of the same year in which the option was exercised. The spread doesn't have to be included in AMT income if the stock is sold within the same year as its exercise.

Qualifying Dispositions of Incentive Stock Options

A qualifying disposition for an ISO is taxed as a capital gain at long-term capital gains tax rates and on the difference between the selling price and the cost of the option.

Disqualifying Dispositions of Incentive Stock Options

A disqualifying or non-qualifying disposition of ISO shares is any disposition other than a qualifying disposition. Disqualifying ISO dispositions are taxed in two ways: as compensation income (subject to ordinary income rates) and as capital gain or loss (subject to the short-term or long-term capital gains rates).

The amount of compensation income is determined as follows:

  • The compensation income is the spread between the stock's fair market value when the option was exercised and the option's strike price if the ISO is sold at a profit.
  • Any profit above compensation income is capital gain.
  • The entire amount is a capital loss, and there is no compensation income to report if the ISO shares are sold at a loss.

Withholding and Estimating Taxes

Those who sell ISO shares may have significant tax liabilities not covered by payroll withholding. Taxpayers should send in estimated tax payments to avoid having a balance due on their tax returns. Taxpayers may also want to increase the amount of withholding instead of making estimated payments.

Note

Employers aren't required to withhold taxes on the exercise or sale of incentive stock options, so those who have exercised but not yet sold ISO shares at the end of the year may have incurred alternative minimum tax liabilities.

Reporting Requirements

ISOs are reported on Form 1040. How they're reported depends on the type of disposition. There are three possible tax reporting scenarios.

Reporting the Exercise of Incentive Stock Options and Shares Not Sold in the Same Year

AMT income is increased by the spread between the fair market value of the shares and the exercise price in this case. This amount can be found using data found on Form 3921 provided by your employer.

  • First, find the fair market value of the unsold shares (IRS Form 3921, box 4 multiplied by box 5).
  • Then subtract the cost of those shares (Form 3921, box 3 multiplied by box 5).
  • The result is the spread. This is reported on IRS Form 6251, line 2i.

Income is being recognized for AMT purposes, so there's a different cost basis in the shares for AMT than the shares for regular income tax purposes. It's a good idea to keep track of this AMT cost basis for future reference. For regular tax purposes, the cost basis of the ISO shares is the price paid. This is the exercise or strike price. For AMT purposes, the cost basis is the strike price plus the AMT adjustment. This is the amount reported on Form 6251, line 2i.

Note

The cost basis of the ISO shares is the price paid for regular tax purposes: the exercise or strike price. It's the strike price plus the AMT adjustment, the amount reported on Form 6251, line 2i, for AMT purposes.

Reporting a Qualifying Disposition of ISO Shares

The gain should be reported on Schedule D and IRS Form 8949. The gross proceeds from the sale are required. This information is provided by the broker on Form 1099-B.

The regular cost basis must also be reported. This figure is the exercise or strike price, found on Form 3921. A separate Schedule D and Form 8949 should be completed to find the capital gain or loss for AMT purposes.

Report gross proceeds from the sale and the AMT cost basis on the separate Schedule D form. This is the exercise price plus any prior AMT adjustment. IRS Form 6251 will have a negative adjustment on line 2k to reflect the difference in gain or loss between the regular and AMT gain calculations. Refer to the 2021 Instructions for Form 6251 for details.

Reporting a Disqualifying Disposition of ISO Shares

Compensation income is reported as wages on IRS Form 1040, line 1. Any capital gain or loss is reported on Schedule D and Form 8949.

Your compensation income may already be included on Form W-2, the employer's wage and tax statement. If so, it should appear in the amount shown in box 1. Sometimes employers will provide a detailed analysis of this amount at the top portion of the W-2. Simply report wages from box 1 on line 1 of your Form 1040 if compensation income is included on the W-2.

Calculate compensation income. Include this amount as wages on line 1 of Form 1040 in addition to the amounts from Form W-2 if the compensation income has not already been included on the W-2.

Report the gross proceeds from the sale of ISO shares on Schedule D and IRS Form 8949. This figure appears on Form 1099-B that you should have received from your broker. You'll also show the cost basis for the shares. The cost basis will be the strike price found on Form 3921 plus any compensation income reported as wages for disqualifying dispositions of ISO shares.

The cost basis will be different if you sold ISO shares in a year other than the ISO exercised year. Complete a separate Schedule D and Form 8949 to report the different AMT gain. Use Form 6251 to report a negative adjustment for the difference between the AMT gain and the regular capital gain.

IRS Form 3921

IRS Form 3921 is used to provide employees with information relating to incentive stock options that were exercised during the year. Employers will provide the employee with one copy of this document for each exercise of ISOs during the calendar year. You may receive multiple 3921 documents or a consolidated statement showing all your exercises if you had two or more exercises.

The formatting of this tax document may vary. But it will contain the following information:

  • Identity of the company transferring stock under the ISO
  • Employee's identity who exercised the ISO
  • The date the incentive stock option was granted
  • The date the incentive stock option was exercised
  • The exercise price per share
  • The fair market value per share on the exercise date
  • The number of shares acquired

This information is used to arrive at the cost basis for the shares, the amount of income that needs to be reported for the alternative minimum tax, the amount of compensation income on a disqualifying disposition, and to identify the beginning and end of the special holding period to qualify for preferred tax treatment.

Identifying the Qualifying Holding Period

ISOs have a special holding period to qualify for capital gains tax treatment. The holding period is two years from the grant date and one year after the stock was transferred to the employee.

IRS Form 3921 shows the grant date in box 1. It shows the transfer date or exercise date in box 2. Add two years to the date in box 1, and add one year to the date in box 2.

It's a qualifying disposition if the ISO shares are sold after the later date. Any profit or loss will be a capital gain or loss taxed at the long-term capital gains rates. It's a disqualifying disposition if the ISO shares are sold at any time before or on this date. The income from the sale is taxed partly as compensation income at the ordinary income tax rates and partly as capital gain or loss.

Calculating Income for the AMT

Report additional income for the AMT if an ISO is exercised and the shares are not sold before the end of the calendar year. The amount included for AMT purposes is the difference between the fair market value of the stock and the cost of the incentive stock option on form 3921.

  • Fair market value per share appears in box 4.
  • Per-share cost of the ISO (its exercise price) is in box 3.
  • The number of shares purchased is in box 5.

Multiply the amount in box 4 by the number of unsold shares to find the amount to include as income for AMT purposes. It's often the same as what's reported in box 5. Subtract the exercise price from this product from box 3 multiplied by the number of unsold shares. This is often the same amount that's shown in box 5. Report this amount on Form 6251, line 2i.

Calculating the Cost Basis for Regular Tax

The cost basis of shares acquired through an incentive stock option is the exercise price, shown in box 3. The cost basis for an entire lot of shares is the amount in box 3 multiplied by the number of shares shown in box 5. This figure will be used on Schedule D and Form 8949.

Calculating the Cost Basis for AMT

Shares exercised in one year and sold in a subsequent year have two cost bases: one for regular tax purposes and one for AMT purposes. The AMT cost basis is the regular tax basis plus the AMT income inclusion amount. This figure will be used on a separate Schedule D and Form 8949 for AMT calculations.

Calculating Compensation Income on a Disqualifying Disposition

Some of the gains are taxed as wages subject to ordinary income taxes. If ISO shares are sold during the disqualifying holding period, the remaining gain or loss is taxed as capital gains.

The amount to be included as compensation income. It's included in box 1 of Form W-2 is the spread between the stock's fair market value when you exercised the option and the exercise price. Multiply the fair market value per share (box 4) by the number of shares sold (often the same amount in box 5) to find this. Subtract the exercise price (box 3) multiplied by the number of shares sold from this product.

This compensation income amount is included on Form W-2, box 1. Include this amount as additional wages on Form 1040, line 1 if it's not included on the W-2.

Calculating the Adjusted Cost Basis of a Disqualifying Disposition

Start with the cost basis. Add any amount of compensation. Use this adjusted-cost-basis figure to report a capital gain or loss on Schedule D and Form 8949.

Frequently Asked Questions (FAQs)

How are incentive stock options reported on a W-2?

Incentive stock options aren't usually reported on your W-2. The only time ISOs will be reported on your W-2 is if you make a disqualifying disposition by selling or gifting the stock before the required holding periods. The value of the sale or gift will appear on your W-2 as compensation income in this case.

How do incentive stock options work?

Companies offer incentive stock options to their employees to encourage productivity and long-term employment. Like standard stock options, they come with a "strike price." This often allows the option holder to buy the underlying stock at a discount. Unlike standard stock options, ISOs have a vesting period that prevents them from being exercised for a time as an incentive for the employee to stay with the company.

The options are exercised. The employee buys the shares at the strike price and is free to sell them at the full market price or keep them in their portfolio as a long-term investment when the vesting period ends.

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Sources
The Balance uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. U.S. Securities and Exchange Commission. "Employee Stock Options Plans."

  2. Block Advisors. "What Are Incentive Stock Options?"

  3. Cornell Law School Legal Information Institute. "U.S. Code § 422. Incentive Stock Options."

  4. IRS. "Topic No. 427 Stock Options."

  5. IRS. "Publication 525, Taxable and Nontaxable Income."

  6. IRS. "Form 3921, Exercise of an Incentive Stock Option Under Section 422(b)."

  7. IRS. "2021 Instructions for Form 6251: Alternative Minimum Tax—Individuals," Page 4.

  8. IRS. "Schedule D: Capital Gains and Losses."

  9. IRS. "Form 8949: Sales and Other Dispositions of Capital Assets."

  10. IRS. "Form W-2."

  11. IRS. "Form 1040, U.S. Individual Income Tax Return."

  12. IRS. "Form 6251: Alternative Minimum Tax—Individuals."

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