Strike Price
The strike price (also called the exercise price) is the predetermined price at which the holder of an option has the right to buy (call option) or sell (put option) the underlying asset upon exercise. It is fixed at contract inception and does not change over the life of the option.
Key takeaways
- For a call option, the holder profits when the underlying price exceeds the strike price; for a put option, the holder profits when the underlying price falls below the strike price.
- The relationship between the strike price and the current market price determines whether an option is in-the-money (ITM), at-the-money (ATM), or out-of-the-money (OTM).
- Strike price selection significantly affects option premium, Greeks, and the probability of profitable exercise, making it a critical component of options strategy construction.
- Options on the same underlying with different strike prices but the same expiration are listed across a 'strike chain,' allowing investors to construct spread strategies.
- For interest rate options such as caps and floors, the strike price is expressed as a rate (e.g., 5%) rather than a dollar price.
Explanation
The strike price is the contractual fulcrum of every options trade, defining the threshold at which value is created or destroyed at expiration. For a European call option, the payoff at expiration is max(S_T − K, 0), where S_T is the underlying price at expiration and K is the strike price. The option has intrinsic value equal to S_T − K when S_T > K (in-the-money) and zero intrinsic value when S_T ≤ K. For a put option, the payoff is max(K − S_T, 0), generating intrinsic value when the underlying falls below the strike.
The classification of options by moneyness relative to the strike price is fundamental to options analysis. An at-the-money (ATM) option has a strike equal (or approximately equal) to the current spot price, maximizing time value and gamma. An in-the-money (ITM) option has positive intrinsic value—its delta is closer to 1 (for calls) or −1 (for puts)—and behaves more like the underlying asset. An out-of-the-money (OTM) option has zero intrinsic value, consisting entirely of time value; it has lower delta and premium, but higher gamma per dollar of premium and higher leverage per dollar invested.
The pricing of options at different strikes is not symmetric. In equity markets, the implied volatility surface exhibits a skew (often called the 'volatility smile' or 'volatility smirk') whereby OTM puts trade at higher implied volatility than ATM or OTM calls. This skew reflects the asymmetric demand for downside protection relative to upside participation, as well as the empirical negative skewness of equity returns. Traders express views on this skew through risk reversals (buying one strike, selling another at equal delta) and butterfly spreads (buying the wings, selling the body).
For structured products and interest rate derivatives, the concept of strike extends naturally to rate-based instruments. In interest rate caps, each caplet has a strike rate—the cap rate—above which the seller pays the difference between the floating reference rate and the strike, scaled by notional and day count. In swaptions, the strike represents the fixed rate of the underlying swap the option grants the right to enter. In these contexts, the strike rate is chosen relative to the current forward rate of the relevant instrument, and the moneyness classification applies analogously.
From a risk management perspective, the choice of strike price in an options hedging program involves an explicit tradeoff between protection level and premium cost. A portfolio manager buying equity put protection at a 90% strike (10% OTM) pays significantly less premium than buying at-the-money puts but sacrifices the first 10% of downside protection. Selecting the optimal strike involves analyzing the portfolio's loss distribution, the cost of protection at various strikes, and the acceptable level of co-insurance (self-retention of losses).
Formula
Call Payoff = max(S_T − K, 0); Put Payoff = max(K − S_T, 0)
Example
An investor owns 1,000 shares of Microsoft (MSFT) trading at $400. To protect against a 15% decline over the next three months, the investor purchases 10 put option contracts (each covering 100 shares) with a strike price of $340 (15% OTM) expiring in three months, paying a premium of $3.50 per share, or $3,500 total. If MSFT falls to $300 at expiration, the put is exercised: the investor can sell 1,000 shares at $340 instead of the market price of $300, limiting the loss per share to $400 − $340 + $3.50 = $63.50 instead of $100. The strike price of $340 thus defines the floor below which the hedge provides protection, net of the premium paid.
Related terms
At The Money Call Option Cap Caplet Delta Equity Floor Gamma Hedging Implied Volatility Implied Volatility Surface In The Money