STT on Options: The Expiry-Day Trap

Every expiry day, the same warning does the rounds on trading groups: "Square off your ITM options before the close, or STT will wipe out your gains." It gets forwarded so often that most traders obey it without ever understanding it.

That's a problem. A rule you follow blindly is a rule you'll eventually break — usually on the one day it matters. So let's actually understand what STT is, why expiry day is different, and exactly how much damage the trap can do in 2026.

A handful of words will keep coming up. Here is what each one means, in plain language — keep this box handy as you read.

What STT Actually Is — and When It Hits

STT — Securities Transaction Tax — is a small government tax on stock market trades, collected automatically by the exchange every time you transact.

You never pay it as a separate bill. It's deducted inside your contract note, bundled with brokerage and exchange fees. Most traders never look closely — which is exactly why expiry day catches them off guard.

For options, there's one rule worth keeping in front of you: in a normal trade, STT is charged on the sell side. Buy an option, and you pay zero STT. Sell it — whether you're booking a profit or writing a fresh position — and STT applies to the premium. The one exception is the whole subject of this article: if you buy an option and let it expire in the money instead of selling it, exercise can trigger STT too. Hold that thought.

The rate matters, because it has been climbing fast. After Budget 2026, STT on the sale of an option is 0.15% of the premium, effective 1 April 2026. That is more than double what it was just sixteen months earlier.

The Trap: When an Option Gets Exercised Instead of Sold

There are only two ways an option position ends: you close it yourself, or the exchange closes it for you at expiry.

Close it yourself — square off — and it's a normal sell trade. STT is 0.15% on the premium you receive. Clean, predictable, small.

Do nothing, and expiry day decides for you. If your option finishes in the money — a call below spot, a put above spot — it isn't allowed to simply lapse. It is automatically exercised. And exercise is taxed differently from a sale.

This is the part beginners miss. They think "I never sold, so there's no STT." But an exercised option is still a taxable event — the tax just lands on a different number, at a different moment, often after you've stopped watching the screen.

Why This Used to Be a Disaster — and What Changed

The expiry-day trap has a real horror-story past — and that past explains why the warning still circulates today.

Before September 2019, STT on an exercised option was charged on the full settlement price of the contract — strike plus intrinsic value, the entire notional amount. On an index trading in the thousands, multiplied by the lot size, that number was enormous.

Traders genuinely made a small profit on a trade and then watched STT alone turn it into a loss. A few hundred rupees of gain, wiped out by an STT bill several times larger. That is the story the warning was built on.

• Up to Aug 2019 · The brutal era

  STT on the full settlement price

  An ITM option carried to expiry was taxed on the entire contract value. Tiny profits routinely turned negative after tax, and traders dumped ITM options near the close — draining expiry-day liquidity.

• Sept 2019 · The big fix

  Exercise STT moved to intrinsic value

  The government restricted exercise STT to the difference between settlement and strike price — the intrinsic value alone. For cash-settled index options, this defused the worst of the trap.

• Oct 2024 · First hike

  Option-sale STT raised to 0.10%

  Budget 2024 lifted STT on option sales from 0.0625% to 0.10% of the premium, aimed at cooling India's runaway derivatives boom.

• Apr 2026 · Second hike

  Sale and exercise STT raised to 0.15%

  Budget 2026 raised both the sale rate and the exercise rate on options to 0.15%. Getting expiry day wrong is now pricier than it has ever been.

So the headline trap — STT bigger than your entire profit on an index option — is largely history. But "largely" is doing some work in that sentence. The trap didn't disappear. It moved.

Index Options and Stock Options Are Not the Same Risk

Here is the distinction that decides whether expiry day is harmless or expensive: how your option is settled.

Index options — Nifty, Bank Nifty, Sensex — are cash-settled. If your option finishes ITM, the exchange simply credits the intrinsic value to you as cash and charges 0.15% STT on that intrinsic value. Nothing changes hands except money.

Stock options — Reliance, HDFC Bank, any single stock — are physically settled. An ITM stock option at expiry is not cashed out. It turns into an actual delivery of shares.

That one word — delivery — is the whole trap. The position is now treated like an ordinary equity transaction, so STT is charged at the 0.10% delivery rate on the full value of the shares, not on the small intrinsic value.

The numbers make it concrete. Picture a stock option where the underlying shares are worth ₹7.5 lakh. Let it expire ITM and the delivery STT alone is roughly ₹750 — calculated on that ₹7.5 lakh, not on a ₹3,000 profit.

And STT is only the first bill. Physical settlement also means you need the full cash to take delivery (or the full shares to give it), and most brokers charge a much steeper brokerage on physically-settled positions than on a normal trade.

Run the Numbers Yourself

Numbers land harder than warnings, so here is a calculator you can poke at.

Pick whether you're holding an index option or a stock option, enter the strike, the settlement price at expiry, the premium you paid, and the lot size. It compares the STT you'd pay by squaring off against the STT if you let the option run to settlement.

Try it with an index option first. You'll see the two STT figures land almost on top of each other — that's the 2019 reform doing its job. A Nifty option that's ITM costs about the same to exercise as to sell.

Now switch to a stock option and watch the "let it expire" number jump. Same intrinsic value, same profit — but the STT is suddenly calculated on the full contract value, and the gap is no longer a rounding error.

This is also why your trade plan should account for costs before you enter, not after. STT, brokerage, and exchange fees aren't noise around a trade — on a thin options scalp, they can be the whole difference between a positive and a negative system.

How to Stay Out of the Trap

When you are holding an option into expiry, every situation reduces to one of three outcomes. Here is the entire decision in one picture:

The flowchart makes the priority obvious: an in-the-money stock option is the one case that demands action. Beyond that, staying safe comes down to four simple habits.

1. Square off ITM options before the expiry-day close. Treat the closing bell as a hard deadline, not a suggestion. If a position is in the money and you don't intend to take delivery, close it.
2. Treat stock options with extra caution. Index options are forgiving; stock options are not. If you hold an ITM stock option near expiry, closing it is almost always the right call — unless you genuinely want the shares.
3. Watch liquidity on deep ITM strikes. Far in-the-money options can turn thin near expiry. Don't wait for the last few minutes — illiquidity can leave you unable to exit at a fair price.
4. Don't count on a "Do Not Exercise" escape route. Earlier, some brokers offered a Do Not Exercise facility for close-to-money stock options. NSE discontinued that facility from the March 2023 expiry, and it has not returned. In today's market there is no opt-out: if you don't want physical settlement, square off the ITM stock option before expiry. Full stop.

None of this needs advanced skill. It needs a routine — and routines are exactly what separate traders who keep their profits from traders who quietly hand them back in fees.