What Is a Stock Plan? Types, Vesting, and Tax Treatment

A stock plan is a compensation program in which your employer gives you a way to own shares of company stock alongside your regular salary. Some plans hand you actual shares over time, some give you the right to buy shares at a locked-in price later, and some let you buy shares at a discount through payroll deductions. The type you receive controls when you owe taxes, what you have to do to keep the equity, and how much of it you actually walk away with.

The Main Types of Stock Plans

Employers use a handful of standard structures. Each has its own rules, and the label on your grant agreement determines almost everything that follows.

Restricted Stock Units (RSUs)

An RSU is a promise from your employer to deliver shares once you meet certain conditions, almost always a vesting schedule tied to time or performance. You don’t own anything until those conditions are satisfied. When the shares vest and land in your brokerage account, the IRS treats their fair market value as ordinary income on that date. Most employers automatically withhold a portion of the shares to cover the tax.

Restricted Stock Awards (RSAs)

RSAs look similar but work differently. You receive actual shares on the grant date, subject to restrictions that prevent you from selling until they vest. The practical difference is that RSAs allow a special tax election (Section 83(b), covered below) that RSUs don’t meaningfully offer.

Incentive Stock Options (ISOs)

An ISO gives you the right to buy company shares at a fixed exercise price, which must be at least the stock’s fair market value on the grant date. ISOs can only be issued to employees, and they expire no later than 10 years from grant. If you own more than 10 percent of the company’s voting stock, the exercise price has to be at least 110 percent of fair market value and the option expires after five years.¹

ISOs carry a $100,000 annual cap. If the total fair market value of stock becoming exercisable for the first time in any calendar year exceeds $100,000 (measured at grant), the excess is treated as non-qualified stock options instead.¹

Non-Qualified Stock Options (NSOs)

NSOs also grant the right to buy shares at a fixed price, but they don’t have to satisfy the strict ISO requirements. That flexibility means NSOs can go to consultants, board members, and advisors, not just employees. The trade-off is less favorable tax treatment: at exercise, the spread between your strike price and the market price counts as ordinary income and is subject to Social Security and Medicare taxes.²

Employee Stock Purchase Plans (ESPPs)

An ESPP lets you buy company stock through after-tax payroll deductions, typically at a discount of up to 15 percent off market price. Federal law sets that ceiling by requiring the purchase price to be no less than 85 percent of fair market value, measured either at the start of the offering period or the purchase date, whichever is lower. You’re limited to purchasing no more than $25,000 of stock per calendar year, based on the stock’s value when the option was granted.³ Most ESPPs run in six-month cycles: you sign up during an enrollment window, choose a contribution percentage (commonly 1 to 15 percent of pay), and the money accumulates until the purchase date, when shares are bought automatically.

How Vesting Works

Vesting is how you earn the right to keep your stock or exercise your options. Until shares vest, they belong to the company on paper, and you’ll forfeit them if you leave. Two structures dominate.

Cliff vesting means nothing vests until a set date, often one year from your start or grant date. If you leave before the cliff, you get zero. After the cliff passes, you might receive 25 percent of your total grant at once, with the rest vesting monthly or quarterly over the following three years.

Graded vesting spreads the schedule more evenly. You might vest 25 percent per year over four years with no cliff, or a small percentage each month. The result is that equity accumulates steadily rather than in a single lump.

Some plans also include acceleration provisions triggered by an acquisition or merger, either automatically at closing or only if you’re terminated within a certain window after the deal.

How Each Type Is Taxed

Tax treatment is the biggest variable between stock plan types. Getting it wrong can trigger a 20 percent accuracy-related penalty on the underpayment.⁴

RSUs and RSAs

When RSUs vest, the fair market value of the delivered shares counts as ordinary income on your W-2 for that year. Your employer withholds federal income tax, Social Security, and Medicare at that point, often by holding back a portion of the shares. If you later sell the shares for more than their vesting-date value, the profit is a capital gain. Hold for at least one year after vesting and the gain qualifies for long-term capital gains rates. RSAs work the same way unless you file an 83(b) election.

Non-Qualified Stock Options

The moment you exercise an NSO, the spread between your strike price and the current market price is ordinary income, and your employer withholds income tax and FICA on that amount.² Any further gain when you sell is a capital gain, with the holding period starting on the exercise date.

Incentive Stock Options

ISOs get more favorable treatment if you’re patient. When you exercise an ISO, no regular income tax is owed on the spread, provided you hold the shares for at least two years after the grant date and one year after the exercise date.⁵¹ Meet both holding periods and the entire profit from exercise through sale is taxed as a long-term capital gain. ISO income is also exempt from Social Security and Medicare taxes.

Sell before satisfying either holding period and you have a disqualifying disposition. The spread at exercise reverts to ordinary income, and you lose the capital gains advantage. Your employer reports the income on Form 3921.⁶

ESPP Shares

ESPP shares have their own holding periods that mirror the ISO rules: at least two years from the offering date and one year from the purchase date to get a qualifying disposition.³ Meet those timelines and the ordinary income portion is limited to the lesser of your actual discount at purchase or the gain on the sale, with everything above that treated as a long-term capital gain. Sell early and the full discount becomes ordinary income regardless of what the stock is doing.

The AMT Trap for ISO Holders

This is where ISO holders get blindsided. Even though exercising an ISO doesn’t trigger regular income tax, the spread at exercise is added to your income for purposes of the Alternative Minimum Tax.⁷ If that adjustment pushes your AMT calculation above your regular tax, you owe the difference. People who exercise a large batch of in-the-money ISOs can end up with a tax bill of tens of thousands of dollars on stock they haven’t sold and might not be able to sell.

For 2026, the AMT exemption is $90,100 for single filers and $140,200 for married couples filing jointly. The exemption begins to phase out at $500,000 and $1,000,000, respectively.⁸ If the spread on your exercise plus your other income stays below the exemption, AMT isn’t a problem. A single large exercise can blow through that threshold.

AMT paid because of an ISO exercise generates a minimum tax credit. You can use it in future years when your regular tax exceeds your tentative minimum tax, gradually recovering the extra tax you paid. The credit carries forward indefinitely.

The Section 83(b) Election

If you receive restricted stock or early-exercise stock options, a Section 83(b) election lets you pay income tax on the stock’s value at the time of transfer rather than waiting until it vests. You file IRS Form 15620 within 30 days of receiving the stock.⁹ Miss that window and the election is permanently unavailable for that grant.

The math works when the stock is worth very little at grant and you expect it to grow. Say you receive restricted shares worth $1 per share and file an 83(b) election. You pay income tax on $1 per share now. If the stock is worth $50 per share when it vests three years later, you’ve avoided paying ordinary income tax on $49 per share. That $49 becomes a capital gain when you sell.

The risk is real. If the stock drops or you leave before vesting and forfeit the shares, you don’t get a refund on the tax you already paid.

What Happens When You Leave

Leaving a job, voluntarily or not, has immediate consequences for unvested equity. Any shares or options that haven’t vested by your last day are typically forfeited. Shares that have already vested and sit in your brokerage account remain yours.

Vested stock options are the time-sensitive piece. Most plans give you a limited window after your departure to exercise, commonly 90 days. For ISOs specifically, the tax code requires you to exercise within three months of leaving to preserve the favorable ISO tax treatment.¹ Let that window close and the options expire, regardless of what they were worth on paper. Termination due to death or permanent disability generally extends the ISO post-termination exercise period to one year.

If you’re planning a career move with a large unvested grant, the vesting schedule alone can be worth tens of thousands of dollars in delayed departure. Run the numbers before giving notice.

1
Office of the Law Revision Counsel. 26 USC 422 – Incentive Stock Options
2
Office of the Law Revision Counsel. 26 USC 83 – Property Transferred in Connection With Performance of Services
3
Office of the Law Revision Counsel. 26 USC 423 – Employee Stock Purchase Plans
4
Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments
5
Office of the Law Revision Counsel. 26 USC 421 – General Rules
6
Internal Revenue Service. About Form 3921 – Exercise of an Incentive Stock Option Under Section 422(b)
7
Office of the Law Revision Counsel. 26 USC 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. Revenue Procedure 2012-29 – Election Under Section 83(b)