Gamma risk means an option’s price can move suddenly, even when Nifty or Bank Nifty barely moves. This happens because delta, which measures how much the option reacts to price changes, starts changing very fast as expiry gets closer. Sellers of naked options feel this the most, especially in the final hours before market close.

What Is Gamma Risk?
Why Gamma Gets Worse Near Expiry
How It Plays Out on Expiry Day
An Illustrative Example With Numbers
What Makes Gamma Risk Different
Why This Knowledge Helps You
What Can Go Wrong
Tips If You Are Trading Expiry
Gamma vs Theta
Mistakes Traders Keep Making
Is This For You?
Conclusion
FAQs

You sell a Bank Nifty strangle on expiry morning. By 11 AM, you are showing a decent profit. You think about holding for a bit more. By 2:30 PM, one sharp move eats into most of that gain. Nothing dramatic happened in the news, but your position fell apart anyway.

That is gamma risk. Delta tells you how much your option price moves when Nifty moves. Gamma tells you how fast that delta itself changes. Near expiry, gamma stops behaving quietly and starts moving fast, which is exactly why expiry trades feel calm one hour and stressful the next.

What Is Gamma Risk?

Delta is the speed of your option. If delta is 0.40, your option moves about 0.40 rupees for every 1 rupee move in the underlying. Gamma tells you how fast that 0.40 changes as the market moves.

Think of driving a car. Delta is your current speed. Gamma is how hard you are pressing the accelerator. When gamma is low, your speed changes gently. When gamma is high, your speed can jump without warning.

Options do not carry the same gamma throughout their life. It stays low when expiry is weeks away and climbs sharply as the last day approaches, especially for strikes sitting close to the current market price.

Why Gamma Gets Worse Near Expiry

An option with three weeks left has time to recover from a bad move. An option with a few hours left does not. That missing time is what pushes gamma higher.

The strikes closest to the current price feel this the hardest. These are called at-the-money strikes, meaning the strike price is close to where Nifty or Bank Nifty is currently trading. According to a published options education resource, an at-the-money option with thirty days left might see its delta shift only slightly, say from 0.50 to 0.55, on a small move in the underlying. With one day left, the same size move can push delta from 0.50 toward 0.80, since the option is suddenly behaving as if it is almost in the money, with far less time left for anything to change.

That single comparison explains why the last day of expiry feels so different from any other trading day.

How It Plays Out on Expiry Day

You take a position. Say you sell a call and a put, expecting the index to stay range-bound.
Morning hours pass calmly. Gamma is present but not aggressive yet, so your profit or loss moves slowly.
Time keeps running out. With every passing hour, less time remains for the trade to work in your favour, and gamma keeps building.
The market makes a move. Even a routine move in Bank Nifty now hits your position differently than it would have earlier in the day.
Your delta shifts fast. An option that reacted mildly at 11 AM can react two or three times harder by 2 PM.
You are forced to react. Hold, hedge, or exit. Waiting too long is usually the costliest choice.

An Illustrative Example With Numbers

To see how this plays out, consider a simplified textbook-style example. A trader sells a Bank Nifty weekly strangle, selling a call around the 24700 strike and a put around the 24450 strike, each for about 15 rupees in premium. Combined, that comes to roughly 9000 rupees in premium collected on one lot, based on a commonly used lot size in this kind of teaching example.

If Bank Nifty stays between the two strikes through the session, both options can expire worthless, letting the seller keep the full premium. This is what the payoff chart below shows.

Early in the day, gamma is moderate, so a routine move of a few dozen points barely dents this payoff. Later in the session, once gamma has built up, the same size move near either strike can shrink the open profit far more sharply, because delta is now changing much faster for those strikes.

The chart below illustrates this general pattern, showing how gamma tends to build from the morning session toward the final hour of trading on expiry day.

A trader who books part of the profit earlier in the day, or converts a naked strangle into a spread by buying a further strike as protection, limits how much that late session move can hurt the position.

What Makes Gamma Risk Different

It is tied to time, not direction. Gamma does not care whether the market goes up or down, only how fast delta shifts.
It is worst at the money. Strikes near the current price carry the highest gamma.
It builds throughout the day. Morning gamma and afternoon gamma on the same expiry day are not the same thing.
It hurts sellers more. Buyers gain from a gamma spike since their potential loss is limited to the premium paid, while naked sellers face losses that can grow quickly.
It does not show up in the option price alone. You will not see gamma risk written on your trading screen. You feel it through how fast your profit or loss moves.

Why This Knowledge Helps You

Once you understand gamma, you stop trusting a trade just because it looked fine an hour ago. You start checking how much time is left, not just where the market is trading.

It also changes how you build a trade. Instead of holding naked strangles right into the close, you start considering spreads, partial exits, and smaller position sizes as expiry nears. Traders who plan around this tend to avoid the kind of sudden, late-session losses that catch naked option sellers off guard.

What Can Go Wrong

The core risk is simple. A small move late in the day can undo a good position faster than most beginners expect, and this is what catches naked sellers off guard most often.

There is a mental trap, too. If the market has stayed quiet for most of the session, it is easy to assume it will stay that way till close. Expiry day does not usually work like that. The last hour is often when gamma is at its highest, and the market can move the fastest.

Liquidity can also thin out on far strikes near the close, so exiting or adjusting a position is not always as smooth as it looks on the option chain. Combine that with a trader unwilling to book a small loss, and gamma risk can turn into a much larger one. This is exactly the kind of risk SEBI has flagged at a market-wide level. In its official disclosure on individual trading in the equity futures and options segment, SEBI has published data showing that a large majority of individual traders in this segment end up with net losses, which is a reminder that leverage and fast-moving risks like gamma need to be respected rather than underestimated.

Tips If You Are Trading Expiry

Trade a smaller size on expiry day compared to a normal trading day.
Avoid holding naked short options into the last hour of trading.
Book part of your profit early instead of waiting for the very last rupee of decay.
Watch how close your strike is to the current spot price, since that determines your gamma exposure.
Set your exit point before you enter the trade, not after it turns against you.
Consider rolling a risky position to a later expiry if it is under pressure, rather than holding it through a volatile close.

Gamma vs Theta

Aspect	Gamma	Theta
What it measures	How fast does delta change	How fast option value fall with time
Behaviour near expiry	Rises sharply	Also rises sharply
Who it favours	Buyers, when the market moves sharply	Sellers, when the market stays quiet
Main risk	Suddenly, large swings in profit or loss	Slow loss of value if you are buying options

These two work against each other on expiry day. Theta makes holding a position feel rewarding since the premium keeps shrinking. Gamma is what can undo that reward in one sharp move. A trade can look safe because of theta and still be risky because of gamma, since both peak around the same time.

Mistakes Traders Keep Making

Holding till the close out of habit. The last hour usually carries the highest gamma of the day.
Using regular position size on expiry day. The same size that felt fine on a normal day can hurt more when moves are sharper.
Ignoring the money strikes. These change values the fastest and deserve the closest attention.
Skipping partial profit booking. Waiting for the last bit of decay often costs more than it earns.
Trading without deciding on an exit level first. No plan means reacting under pressure, which rarely goes well.
Treating expiry day as easy money. It rewards discipline far more than excitement.

Is This For You?

If you actively trade Nifty or Bank Nifty options, especially as a seller, gamma risk is something you will run into on nearly every weekly expiry. Understanding it is not optional at that point.

If you are a long-term investor who occasionally buys options for hedging, this matters less on a day-to-day basis, but it is still worth knowing before touching expiry week contracts. If you are just starting with options, it helps to learn delta and theta first, watch a few expiry sessions without trading, and come back to gamma once the basics feel familiar.

Conclusion

Gamma risk explains why an option position can look fine at noon and fall apart by mid-afternoon without any dramatic news. It builds through the day, peaks near the money, and hits naked sellers the hardest.

The response to it is not complicated. Trade smaller, prefer spreads over naked positions, and book profit earlier rather than later. Once you start watching for gamma instead of being surprised by it, expiry day trading becomes far easier to read.