Strike Price

The strike price (also exercise price) is the fixed price at which a call option holder has the right to buy or a put option holder has the right to sell the underlying asset. The strike is set when the option is issued and does not change during the option’s life. It is one of the two key determinants of an option’s value and profitability, along with the underlying asset’s current price.

The role of strike in option value

The strike price is the pivot point for all option economics. For a call option, the further the stock price is above the strike, the more intrinsic value the call has. For a put option, the further the stock price is below the strike, the more intrinsic value the put has.

If you own a call struck at $100 and the stock is at $110, the call has $10 of intrinsic value. If the stock falls to $95, the intrinsic value is $0—the call has no value related to the current stock price, though it still has time value until expiration date.

The strike is the level where the option “tips” from worthless to valuable (or vice versa). For a call, every dollar above the strike is profit; every dollar below the strike is loss (of the premium paid). For a put, every dollar below the strike is profit; every dollar above the strike is loss.

Strike selection and cost

Higher strike prices on calls are cheaper because they are further out-of-the-money and less likely to finish profitably. A $110 call on a $100 stock costs less than a $100 call, which costs less than a $90 call.

Conversely, lower strike prices on puts are cheaper because they are further out-of-the-money. A $80 put on a $100 stock costs less than a $90 put, which costs less than a $100 put.

This creates a trade-off for investors. A cheap $120 call on a $100 stock has limited payoff potential (you profit only if the stock rises above $120). An expensive $100 call has lower breakeven (stock only needs to rise above $100 + call premium). The strike selection encodes your conviction in the move size.

In-the-money, at-the-money, out-of-the-money

An option’s position relative to the strike is described in three states:

• In-the-money (ITM): A call is ITM if the spot price exceeds the strike. A put is ITM if the spot price is below the strike. The option has intrinsic value.
• At-the-money (ATM): The spot price equals the strike. The option has no intrinsic value, only time value.
• Out-of-the-money (OTM): A call is OTM if the spot price is below the strike. A put is OTM if the spot price is above the strike. The option is worthless at expiration if the stock does not move.

Strike spacing and available strikes

For a stock trading above $250, strikes typically come in $2.50 or $5 increments (e.g., $250, $252.50, $255, $257.50). For stocks below $250, strikes usually come in $1 increments ($100, $101, $102). For very cheap stocks, strikes might be $0.50 apart.

This spacing allows traders to fine-tune the strike price to their view while keeping the options exchange manageable. Too many strikes create illiquidity; too few make hedging imprecise.

Strike and the Greeks

The delta of an option—how much the option price moves for each $1 move in the stock—depends heavily on the strike relative to the spot. A deep-in-the-money call has a delta near 1.0 (moves almost dollar-for-dollar with the stock). An at-the-money call has a delta around 0.5. A deep out-of-the-money call has a delta near 0.

Gamma (how delta changes) is highest at-the-money and falls toward zero far from the strike. Theta (time decay) is typically negative for long option positions and concentrated around at-the-money strikes. Vega (sensitivity to volatility) is highest at-the-money.

Strike, volatility smile, and implied volatility

The implied volatility of an option depends not just on the underlying stock’s historical volatility but also on the strike relative to the spot. Out-of-the-money put strikes typically have higher implied volatility than at-the-money strikes, reflecting the market’s fear of crashes. This creates the volatility smile or volatility skew—different strikes have different implied volatility levels.

A trader using the Black-Scholes model or other pricing models must account for the strike’s effect on implied volatility, not just its mathematical effect on intrinsic value.

Strikes in bonds, swaps, and other derivatives

The strike concept extends beyond stock options. A interest-rate-swap swaption has a strike rate (the fixed leg rate you have the right to lock in). A currency swap option has a strike exchange rate. The principle is the same: the strike is the level at which the option becomes profitable.

See also