At-the-money

Moneyness asks one question: if I could exercise this option right now, would money come to me? In-the-money says yes. Out-of-the-money says no. At-the-money says neither — the strike and the spot are the same number, so exercising is pointless in both directions.

In practice they are almost never exactly equal. Strikes sit at fixed intervals — Rs 5, Rs 10, Rs 50 — while the spot moves in far smaller steps. So the workbook gives the working definition: the at-the-money option is the one whose strike is closest to the spot price, not the one where the two are literally identical.

The important consequence is not the definition but where the money goes. An ATM option has zero intrinsic value. Every rupee of its premium is time-value.

ATM is where uncertainty is greatest, and the premium shows it.

A deep ITM or deep OTM option is, in a sense, already decided. The spot has to travel a long way before an option 250 points in the money stops being in the money. An ATM option is decided by nothing at all: a small move in either direction flips it from ATM to ITM or OTM. That uncertainty is a function of time to expiry and of volatility, and both of those live entirely in the time value.

So the same strike behaves differently for the two contract types at the same instant. With the index below a strike, the call at that strike is OTM while the put at that strike is ITM. Calling a strike "at the money" is a statement about its distance from spot, not about either contract being worthless.

ATM is also the strike where gamma and theta are largest — the delta moves fastest and the time value bleeds fastest, both for the same reason.

ATM strike        = the listed strike nearest to the spot price S
Intrinsic value   = 0            (for both the call and the put)
Time value        = Premium      (the entire premium)

For reference, the two neighbours:

Call is ITM when S > X        Put is ITM when S < X
Call is OTM when S < X        Put is OTM when S > X

Finding the strike. The index is at 18,415 and three strikes are listed: 18,350, 18,400 and 18,450.

18,400 is the ATM option. Not because it equals the spot — it does not — but because nothing listed is nearer.

Now price it. Take the workbook's four-strike chain with the index at 17,562 and a contract size of 50:

The ATM strike here is 17,600, only 38 points from spot. And it carries almost exactly twice the time value of the strike 262 points in the money — Rs 259 against Rs 130.

In rupees, at a lot size of 50: buying the ATM call and put together costs (130 + 167) × 50 = Rs 14,850, of which Rs 12,950 is pure time value that decays to nothing by expiry. The deep-ITM 17,300 pair costs (327 + 65) × 50 = Rs 19,600, of which only Rs 6,500 decays — the other Rs 13,100 is intrinsic value that survives.

You pay more in rupees for the ITM pair and lose less of it to time. That trade-off is the whole of moneyness.

Chapter 16.3 (Moneyness of an option) defines all three states and gives the 18,415 illustration verbatim; Chapter 16.4 supplies the intrinsic-and-time-value split, and Chapter 16.10 explains why ATM carries the greatest uncertainty. Expect a classify-this-option question with a spot and a strike, and a "which option has the highest time value" question — the answer is the at-the-money one.

• ATM does not mean strike equals spot. It means the nearest listed strike. The workbook is explicit that exact equality is rare.
• The same strike is not ATM for everybody at once. As spot drifts, the ATM strike migrates; an option is ATM for a moment, not for a contract life.
• ATM intrinsic value is zero, not small. Intrinsic value can never be negative, because nobody exercises at a loss.
• A strike can be OTM for the call and ITM for the put simultaneously — those are two different contracts, and only one of them can be in the money.
• Highest time value does not mean highest premium. A deep ITM option usually costs more in rupees; it just has less to lose to decay.
• ATM is where time-decay bites hardest. Buying ATM because it looks "fair" ignores that you are buying the fastest-wasting contract on the board.