RSUs vs. Stock Options: How Equity Compensation Actually Works

Equity compensation has become a standard part of pay packages at public and private companies alike, especially in tech, biotech, and other growth sectors. But two of the most common forms—restricted stock units (RSUs) and stock options—work very differently, and confusing them can lead to costly tax surprises or missed decisions. Here's how each actually functions.

RSUs: A Promise of Shares, Taxed at Vesting

A restricted stock unit is a company's promise to give you actual shares of stock once certain conditions are met, typically the passage of time (a vesting schedule) and sometimes performance targets. Unlike options, RSUs don't require you to buy anything. Once they vest, the shares are yours, and their full market value on that date is treated as ordinary income—similar to a cash bonus, but paid in stock.

Because RSU income counts as wages, employers are required to withhold federal, state, and payroll taxes at vesting, per Internal Revenue Service guidance on supplemental wages. Many companies handle this through a 'sell-to-cover' arrangement, automatically selling a portion of the newly vested shares to pay the tax bill, so you receive the net shares remaining. If your employer doesn't withhold enough, you may owe additional tax when you file, and could face estimated-tax penalties if the shortfall is large.

Once RSU shares vest, any further gain or loss from holding them is a capital gain or loss, measured from the vesting-date value (your cost basis) to the eventual sale price. Hold more than a year past vesting and qualifying gains get long-term capital gains treatment; sell sooner and it's short-term, taxed at ordinary rates.

Stock Options: A Bet on Future Appreciation

A stock option gives you the right, but not the obligation, to buy company shares later at a fixed 'strike' or 'exercise' price, set when the option is granted. Options only have value if the stock's market price rises above that strike price. If it doesn't, the options can expire worthless. This is the core difference from RSUs: RSUs have value the moment they vest (assuming any stock price above zero), while options need the stock to climb before they're worth anything.

Two Flavors of Options, Two Tax Regimes

• Nonqualified stock options (NSOs) are the more common and straightforward type. When you exercise an NSO, the difference between the stock's market value and your strike price is taxed immediately as ordinary income, and your employer generally withholds taxes on that spread.
• Incentive stock options (ISOs), available only to employees and subject to strict IRS rules under Internal Revenue Code Section 422, offer potentially favorable tax treatment: no ordinary income tax at exercise. But the spread at exercise can trigger the Alternative Minimum Tax (AMT), a parallel tax system designed to ensure high earners with large deductions or preference items still pay a minimum amount of tax.
• To get ISOs' full benefit—having the entire gain treated as a long-term capital gain—you generally must hold the shares more than one year after exercise and more than two years after the grant date, a 'qualifying disposition.' Selling sooner creates a 'disqualifying disposition,' converting some of the gain back into ordinary income.

The 83(b) Election: A Timing Choice With Real Stakes

Employees who exercise stock options early (before they fully vest) or receive certain restricted stock awards can file an 83(b) election with the IRS within 30 days of the grant or early exercise. This locks in ordinary income tax based on the value at that early date—often very low or zero if the company is young—rather than waiting until vesting, when the value (and tax bill) could be much higher. It's a use-it-or-lose-it, no-extensions deadline, and the election is irreversible, so getting professional tax advice before filing is prudent.

Practical Considerations for Holders

• Vesting schedules matter: a typical four-year vest with a one-year 'cliff' means nothing vests until year one, then portions vest periodically after.
• Concentration risk is real: holding too much employer stock, on top of your salary already depending on that employer, adds correlated risk to your finances.
• Options can expire: most option grants have an expiration window (often 10 years from grant, or a short window after leaving the company), so tracking deadlines is essential.
• Private company equity is harder to value and sell: without a public market, RSUs or options in private firms may be illiquid until an IPO, acquisition, or company-sponsored tender offer.