At-the-Money
An option is at-the-money (ATM) when the strike price is equal or very close to the current market price of the underlying. ATM options on NSE — particularly Nifty and Bank Nifty options — have the highest time value and are typically the most liquid strikes.
At-the-money options occupy the midpoint between in-the-money and out-of-the-money. Because there is equal uncertainty about whether the option will expire in-the-money or out-of-the-money, ATM options carry the highest time value relative to the total premium. Their delta is approximately 0.50 for calls and -0.50 for puts, reflecting this equal probability.
The ATM strike is the reference point for most options strategies. When constructing a straddle or a strangle, the ATM strike determines the central pivot around which the strategy is built. Iron condors are positioned symmetrically around the ATM level, with out-of-the-money options on both sides creating the profit zone.
On NSE, ATM Nifty and Bank Nifty options historically accounted for the majority of daily options volume. Traders, hedgers, and arbitrageurs all gravitated to the ATM strikes because of the liquidity, tight bid-ask spreads, and the balanced risk profile. The ATM implied volatility was also used as the benchmark for quoting the overall options market's expectation of near-term price movement.
A subtlety is that the ATM strike rarely sits exactly on the current price; rather, the nearest available strike to the current price is considered ATM. For Nifty at 18,025, both the 18,000 and 18,050 strikes might be considered near-ATM, with the 18,000 strike typically receiving the higher label because Nifty options were quoted in 50-point intervals.
The high time value of ATM options makes them the primary arena for theta decay strategies. Option sellers who wrote ATM straddles on Nifty were attempting to collect the maximum time value available, betting that the underlying would remain range-bound until expiry. The risk of such strategies was significant if the underlying made a large directional move.