What Is a Stock Option?

Before anything else, separate the two. The first meaning is a tradable options contract: a standardized instrument you buy or sell on an options exchange, like a call on Apple expiring next month. It has a strike price, an expiration date, and a premium, and one standard contract typically controls 100 shares. This is what people mean by “trading options” or “the options market.”

The second meaning is an employee stock option: a form of equity compensation a company grants its workers, giving them the right to buy company shares at a fixed strike price after a vesting period. There is no open market premium to pay and no weekly expiration; instead there is a vesting schedule, a grant of ISOs or NSOs, and tax rules that hinge on when you exercise and sell. The rest of this guide treats the two separately so they do not blur together.

A tradable option is a contract between two parties about a stock's future price. The buyer pays a premium for the right, but not the obligation, to make a trade at the strike price before the option expires. There are two basic types. A call gives the buyer the right to buy the stock at the strike, so it gains value when the stock rises. A put gives the buyer the right to sell the stock at the strike, so it gains value when the stock falls.

The key words are “right, but not the obligation.” If the trade does not work in your favor, you can simply let the option expire and walk away, losing only the premium you paid. That asymmetry, a known, limited cost for a potentially larger payoff, is what makes options appealing and dangerous at once. The seller (or writer) of the option is on the other side: they collect the premium up front but take on the obligation to deliver if the buyer exercises, which is why selling options can carry much larger risk than buying them.

Three terms define every tradable option. The strike price is the fixed price at which the option lets you buy (call) or sell (put) the stock. The expiration date is the deadline after which the option ceases to exist; options come in weekly, monthly, and longer-dated varieties. The premium is what the option costs, quoted per share, so a premium of $2.00 on a standard 100-share contract costs $200.

Whether an option has value at expiration depends on where the stock trades relative to the strike. A call is “in the money” when the stock is above the strike, and a put is in the money when the stock is below it. Otherwise the option is “out of the money” and, at expiration, worthless. For more of this vocabulary, our stock market terminology guide defines the building-block terms, and our what is options trading guide goes deeper on the mechanics of buying and selling contracts.

An option's premium has two parts. Intrinsic value is how much the option is already in the money, the difference between the stock price and the strike. A call with a $100 strike on a stock trading at $108 has $8 of intrinsic value. If the stock is below the strike, intrinsic value is zero, because nobody would exercise the right to buy high.

Time value is everything else in the premium: the extra a buyer pays for the chance the stock moves further in their favor before expiration. It depends heavily on how much time is left and how volatile the stock is, since both raise the odds of a big move. The catch is that time value decays as expiration approaches, a process called time decay. This is why an option can lose value even when the stock barely moves, and why buyers can be right about direction yet still lose money if the move comes too slowly. Pricing models like Black-Scholes formalize this, but the intuition is simply intrinsic value plus a shrinking premium for time and uncertainty.

Investors reach for options for three broad reasons. The first is hedging: buying a put on shares you own works like insurance, capping your loss if the stock drops, in exchange for the premium cost. A fund manager worried about a downturn might buy puts to protect a portfolio rather than sell everything. The second is income: selling a covered call on stock you already hold lets you collect premium up front, the trade-off being that your upside is capped if the stock rallies past the strike.

The third is speculation and leverage: because one contract controls 100 shares for a fraction of their cost, options let a trader bet on a move with less capital than buying the shares outright. That leverage can multiply gains, but it just as easily multiplies losses, and the option can expire worthless. The same leverage that makes options powerful for a small protective hedge makes them a fast way to lose money when used to chase short-term moves.

Options are widely considered advanced instruments, and for good reason. The first risk is expiration: unlike a share you can hold through a rough patch and wait out, an option has a deadline, and an out-of-the-money option at expiration is worth nothing. Buyers routinely lose 100% of the premium they paid. The second risk is leverage, which cuts both ways. A position that controls far more stock than its cost can swing violently, turning a modest stock move into an outsized percentage gain or loss on the option.

The third risk lands on option sellers. Writing options collects premium up front but takes on obligations that can be far larger than that premium. Selling a put obligates you to buy the stock if it falls, and selling an uncovered call exposes you to theoretically unlimited losses if the stock soars. None of this makes options bad, but it does make them tools that reward understanding the downside before the upside. Walnut is informational and not an investment adviser, so treat options as something to learn thoroughly, not a shortcut to returns.

Calls and puts are the two atoms that every options strategy is built from, and covered calls and protective puts are the two most common ways ordinary investors use them around stock they already own. Everything more elaborate, spreads, straddles, and the rest, is just combinations of these pieces. The figures and roles here are illustrative, not advice; the right tool, if any, depends entirely on your situation.

Employee stock options are a different animal. Instead of a market contract, they are a grant from your employer, the right to buy a set number of company shares at a fixed strike price (often the share price on the grant date) after you stay long enough to vest. A typical schedule is four years with a one-year cliff: nothing vests until you have been there a year, then the rest vests gradually. Leave early and unvested options are usually forfeited.

They come in two main flavors that differ on tax. ISOs (incentive stock options) can qualify for favorable long-term capital gains treatment if you meet holding requirements, but they can trigger the alternative minimum tax. NSOs (non-qualified stock options) are taxed as ordinary income on the spread between strike and market price when you exercise. The appeal is the same as a call option in spirit: if the company's share price climbs above your strike, the options are worth the difference; if it never does, they expire with no extra value. Because the tax rules are specific and the stakes can be large, people often work with a tax professional before exercising. Walnut does not handle employee equity and is not a tax adviser.

Walnut is not an options platform, and that is deliberate. It focuses on the part most long-term investors actually live in: building and tracking baskets of stocks and ETFs around a clear thesis, and understanding the portfolio they already hold. If you trade options or hold employee equity, those positions live at your broker and your company; Walnut's job is to help you see and reason about the broader portfolio around them.

It connects your existing brokerage through SnapTrade and lets you ask, in plain language through Claude, ChatGPT, or a built-in assistant, how your holdings are doing, where you are concentrated, and how each position tracks against the S&P 500. It is read-only by default, and you approve any trade before it is placed. Walnut is informational and is not an investment adviser; it helps you understand your own portfolio rather than telling you what to trade.

“Stock option” means two things. A tradable option is a market contract giving you the right, but not the obligation, to buy (call) or sell (put) a stock at a strike price before expiration, for which you pay a premium made of intrinsic value plus decaying time value. An employee stock option is equity compensation, the right to buy company shares at a fixed strike after vesting, granted as ISOs or NSOs with different tax treatment. Both lock in a price, but they trade, expire, and tax in completely different ways.

Whichever meaning applies to you, the honest summary is that options are powerful and risky. Bought options can expire worthless, leverage amplifies losses as readily as gains, and selling options can cost far more than the premium collected. Learn the downside first. To keep building the vocabulary, see our what is options trading and stock market terminology guides. Nothing here is a recommendation; verify specifics and consider professional tax advice before acting.