Option Strike Prices: How It Works, Definition, and Example

What Is a Strike Price?

Options contracts are derivatives that give the holders the right, but not the obligation, to buy or sell some underlying security at some point in the future at a pre-specified price. This price is known as the option's strike price (or exercise price). For call options, the strike price is where the security can be bought by the option holder; for put options, the strike price is the price at which the security can be sold.

An option's value is informed by the difference between the fixed strike price and the market price of the underlying security, known as the option's "moneyness."

For call options, strikes lower than the market price are said to be in-the-money (ITM), since you can exercise the option to buy the stock for less than the market and immediately sell it at the higher market price. Likewise, in-the-money puts are those with strikes higher than the market price, giving the holder the right to sell the option above the current market price. This feature grants ITM options intrinsic value.

Calls with strikes that are higher than the market, or puts with strikes lower than the market, are instead out-of-the-money (OTM), and only have extrinsic value (also known as time value).

Understanding Strike Prices

The strike price is a key variable of call and put options, which defines at which price the option holder can buy or sell the underlying security, respectively.

Options are listed with several strike prices both above and below the current market value. Say that a stock is trading at $100 per share. The $110-strike call option would give the holder the right to buy the stock at $110 on or before the date when the contract expires. This means that the option would lose value if the stock falls and gain in value as the underlying stock increases in price. But if it never reaches $110 before the expiration date, the call will expire worthless. This is because you could buy the stock for less. If the stock did rise above $110, you could still exercise the option to pay $110 even though the market price is higher. (Put options would work similarly but give you the right to sell rather than buy the underlying).

The strike prices listed are also standardized, meaning they are at fixed dollar amounts, such as $31, $32, $33, $100, $105, and so on. They may also have $2.50 intervals, such as $12.50, $15.00, and $17.50. The distance between strikes is known as the strike width. Strike prices and widths are set by the options exchanges.

The Relationship Between Strike Price and the Underlying Security

The price of an options contract is known as its premium, which is the amount of money that the buyer of an option pays to the seller for the right, but not the obligation, to exercise the option. The price difference between the underlying's market price and the strike price determines an option's value in what is known as the moneyness of the option.

The more "in-the-money" an option is, the higher its premium-as the difference between the strike and the underlying gets smaller, options become more valuable, and when the strike becomes greater they are in-the-money. Similarly, an option will lose value as the difference between the strike and underlying price become larger and as the option falls out-of-the-money.

"Moneyness:" The Three Types of Strike Prices

Options can thus be either in-the-money (ITM), out-of-the-money (OTM), or at-the-money (ATM).

For buyers of the call option (such as in the example above), if the strike price is higher than the underlying stock price, the option is out-of-the-money (OTM). In this case, the option doesn't have intrinsic value, but it is likely to still have extrinsic value based on volatility and time until expiration, as either of these two factors could put the option in-the-money in the future. Conversely, If the underlying stock price is above the strike price, the option will have intrinsic value and be in-the-money.

Puts with strike prices higher than the current price will be in-the-money since you can sell the stock higher than the market price and then buy it back for a guaranteed profit. A put option will instead be in-the-money when the underlying stock price is below the strike price and be out-of-the-money when the underlying stock price is above the strike price. Again, an OTM option won't have intrinsic value, but it may still have value based on the volatility of the underlying asset and the time left until option expiration.

Finally, an option with a strike price at or very near to the current market price is known as at-the-money (ATM). ATM options are often the most liquid and active options traded in a name.

Strike Price and Option Delta

An option's delta is how much its premium will change given a $1 move in the underlying. So, a call with a +0.40 delta will rise by 40 cents if the underlying rises by a dollar.

At-the-money calls have a delta of +0.50; at-the-money puts have a delta of -0.50. Options that are in-the-money will have deltas greater than 0.50 (positively for calls, negatively for puts), and out-of-the-money options will have deltas less than 0.50.

An option with a delta of 1.00 is so deep in-the-money that it essentially behaves like the stock itself. Examples would be call options very far below the current price and puts with strikes very high above it. Conversely, deep out-of-the-money options have deltas very close to zero and are essentially worthless because they are calls that have strikes so high above the market, or puts with strikes so far below it, that it is extremely unlikely they will ever be in the money before expiry.

What Determines an Options Value

Pricing models were developed in the 1970s and '80s to help understand the fair value of an options contract, such as the Black-Scholes Model and the Binomial Tree Model. Theoretically, an options' premium should be related to the probability that it finishes in-the-money. The higher that probability, the greater the value of the right that the option grants.

Regardless of what model is used, options prices always depend on the following five inputs

• market price
• strike price
• time to expiration
• interest rates
• volatility
• dividends (if applicable)

We've already seen how the difference between the market price and the strike price fits into the equation. The time to expiration and volatility inputs indicate how likely it is for an option to finish in-the-money before it expires. The more time there is to go, and/or the more volatile the underlying price moves are, the more likely that the market price will reach the strike price. Volatile moves happen due to acquisitions, earnings reports, company news, and other factors. Therefore, options with longer times until expiration and those with greater volatility will have higher premiums.

Strike Price Example

Assume there are two option contracts. One is a call option with a $100 strike price. The other is a call option with a $150 strike price. The current price of the underlying stock is $145. Assume both call options are the same; the only difference is the strike price.

• At expiration, the first contract is worth $45. That is, it is in-the-money by $45. This is because the stock is trading $45 higher than the strike price.
• The second contract is out-of-the-money by $5. If the price of the underlying asset is below the call's strike price at expiration, the option expires worthless.

If we have two put options, both about to expire, and one has a strike price of $40 and the other has a strike price of $50, we can look to the current stock price to see which option has value. If the underlying stock is trading at $45, the $50 put option has a $5 value. This is because the underlying stock is below the strike price of the put.

The $40 put option has no value because the underlying stock is above the strike price. Recall that put options allow the option buyer to sell at the strike price. There is no point using the option to sell at $40 when they can sell at $45 in the stock market. Therefore, the $40 strike price put is worthless at expiration.

The Bottom Line

An option's strike price tells you at what price you can buy (in the case of a call) or sell (for a put) the underlying security before the contract expires. The difference between the strike price and the current market price is called the option's "moneyness," a measure of its intrinsic value. In-the-money options have intrinsic value since they can be exercised at a strike price that is more favorable than the current market price, for a guaranteed profit. Out-of-the-money options do not have intrinsic value, but still contain extrinsic, or time value since the underlying may move to the strike before expiration. At-the-money options have strikes at or very close to the current market price and are often the most liquid and active contracts in a name.