The STT Exercise Trap: Why Holding ITM Options to Expiry Can Eat Your Profit
You're long 24800 CE, expiry day, spot's at 25000. Premium is trading around 195. You're sitting on a decent profit and you think — why pay the spread to exit? Let it expire, pocket the intrinsic. 200 points times 75 lots is 15,000.
That's the trap.
If you don't square off and the option expires ITM, STT on exercised options is charged at 0.125% of the intrinsic value of the entire contract, not on the premium. Most people read that line and don't actually do the math. Let's do it.
Intrinsic = 200 points × 75 = 15,000. That's per lot. But STT is on the notional settlement, which is strike + intrinsic essentially — the calculation runs on (intrinsic × lot size) at 0.125%. For our 24800 CE settling at 25000:
- Settlement value the exchange uses: 25000 × 75 = 18,75,000
- STT at 0.125% on exercised ITM options: ₹2,343
Versus selling the option in the market at 195. STT on sell side of options is 0.1% on premium: 195 × 75 × 0.001 = ₹14.6.
That's ₹2,343 vs ₹14. You just handed back roughly 16% of your profit because you didn't click sell.
It gets worse the deeper ITM you go
The STT scales with the strike, not the profit. A 24000 CE expiring at 25000 with spot at 25000:
- Intrinsic profit: 1000 × 75 = 75,000
- STT on exercise: 25000 × 75 × 0.00125 = ₹2,343
Still roughly the same STT bill, smaller as a percentage. So the trap bites hardest on the marginally-ITM stuff — exactly the strikes retail tends to hold through.
The "just barely ITM" disaster
This is where people actually lose money on a winning trade. Bought 25000 CE for 80. Spot closes at 25030. Intrinsic is 30 — that's 2,250 per lot gross, minus your 80 premium paid (6,000), you're already down on the trade. Now add ₹2,346 STT on exercise. You turned a small loss into a brutal one by not selling at 25-30 in the last hour.
Sell it. Even at 20. Even at 15. The market exit fee is nothing compared to physical settlement STT.
What to actually do
Square off ITM longs before 3:30 on expiry. If liquidity is bad in the last 15 minutes (it often is for far-from-ATM strikes), do it by 3:00. The bid-ask spread you eat is almost always cheaper than the STT.
If you want to see what your actual take-home looks like after STT, brokerage, GST and the rest on different exit scenarios, I keep one open at /options-profit-calculator-india — plug in exercise vs market sell and the gap is obvious.
The exchange isn't hiding this. It's in the contract note. People just don't read it until it's too late.