What does "at the money" mean?
An option is "at the money" (ATM) when its strike price is roughly equal to the current stock price. In practice, traders refer to the nearest strike above or below the market price as ATM because exact matches are rare.
How ATM options behave
ATM options sit at the intersection of two forces:
- They have no intrinsic value yet, so they are cheaper than ITM options.
- They have the highest extrinsic value of any strike, because the market is unsure which direction they will go. Maximum time value, maximum time decay.
ATM options also have the highest gamma, meaning their delta changes fastest as the stock moves. A small move past the strike can turn a 50-delta option into a 70-delta option in minutes.
When to use ATM strikes
ATM strikes are a reasonable default when you have a directional bias but no view on how fast or far the move will be. They cost more than OTM strikes but decay slower as a percentage of their price, and they gain the most when the stock starts trending.