At the Money (ATM)

An option is at the money when the strike is equal to or very close to the current market price of the underlying. Technically the strike is never exactly at spot, so ATM usually refers to the nearest-strike option.

ATM options have the highest time value of all strikes at the same expiration, because the outcome is most uncertain. Their delta is approximately 0.50 for calls and −0.50 for puts.

ATM options are the most liquid strike for most underlyings and are commonly used to measure implied volatility — the ATM straddle price implies expected move.