ATM, ITM, OTM: choosing a strike and what it changes

You have decided SENSEX is going up. Good. Now the broker screen asks you a second question that nobody prepared you for: which strike?

78,000. 78,100. 77,600. They all say "CE". One costs ₹340, one costs ₹95, one costs ₹22. Most people pick the ₹22 one, because ₹22 × 20 = ₹440 and that feels safe.

It is not safe. It is the most common way retail money quietly disappears on a Thursday.

Every option price is two things glued together

Take SENSEX at 78,000 and a 77,600 call. If you exercised it right now, it would be worth 400 points, because you hold the right to buy at 77,600 something trading at 78,000. That 400 is intrinsic value. It is real. It exists whether the market moves or not.

If that option is quoting 460, the extra 60 is time value. That is the market charging you for the possibility of further movement before Thursday. Time value is not real in the same way. It melts. Every hour of every day, it gets smaller, and on expiry afternoon it goes to zero.

Those two words explain the entire ATM / ITM / OTM question.

The three names

• ITM (in the money) — for a call, a strike below the current index. Has intrinsic value. Expensive. Moves closely with the index.
• ATM (at the money) — the strike nearest the current index. Almost no intrinsic value, the maximum possible time value. This is the most actively traded strike.
• OTM (out of the money) — for a call, a strike above the index. Zero intrinsic value. Cheap. It is pure time value, which means it is pure melting ice.

For puts, flip it: a put is ITM when the strike is above the index.

The auto-rickshaw way to think about it

An auto ride across town costs ₹180. A ride two lanes down costs ₹20. The ₹20 ride is cheaper, obviously. It also does not take you anywhere useful.

A far OTM option is the ₹20 ride. You paid a small amount, so the loss feels small — but you needed the index to travel a long distance, in your direction, before Thursday, just to break even. If SENSEX moves 200 points in your favour and your strike needed 500, you were right about the direction and you still lost everything.

What changes when you change strike

That last row costs more than people realise. A SENSEX lot is 20 quantity, and our positions run several lots. If a strike quotes 21.00 bid and 24.00 ask, you have lost 3 points the instant you enter — before the market has done anything at all. ATM and near-ITM strikes have the tightest spreads because that is where the volume sits.

Roughly how much it moves

There is a number called delta that tells you how much the option premium moves for a 1-point move in SENSEX. An ATM option sits near 0.50 — the index moves 100 points, the premium moves roughly 50. A deep ITM option approaches 1.00, so it tracks the index almost point for point. A far OTM option might be 0.10, which means a 100-point move in your favour earns you about 10 points of premium. Meanwhile decay is taking points away in the other direction.

On expiry Thursday, these effects go extreme. A far OTM strike can sit motionless through a genuine rally and then expire worthless in the last hour.

Where our own machine sits

We used to trade ATM strikes. Since 21 August our live lane trades roughly one strike in the money instead. The reason was not a prediction — it was that ATM premiums move too much on small index wiggles, and a slightly ITM strike carries real intrinsic value that does not evaporate while a trade develops. It is not the "better" choice for everyone; it is the choice that matched our stop-loss size and our capital.

The short version: cheap is not the same as good value. What you are actually choosing when you pick a strike is how much of your premium is real and how much is hope. Decide that on purpose.