Why option buyers pay almost no STT on entry but get crushed on ITM exercise — and how option sellers pay differently. The single biggest retail F&O blind spot.
Securities Transaction Tax (STT) on options doesn't work the way most retail traders assume. The rate structure for buyers and sellers is asymmetric, and the auto-exercise rule on ITM options at expiry produces the single most-common retail F&O surprise.
Understanding STT mechanics is the difference between profitable options trading and a slow bleed. The taxes are small per trade in absolute terms but compound viciously over time, and the ITM exercise rule can wipe out an otherwise-profitable expiry-day trade.
On entry: 0.05% on the premium paid. Buying a NIFTY 22,000 CE for ₹100 premium incurs ₹0.05 × premium × lot = ₹0.05 × 100 × 25 = ₹125 STT (assuming 25 lot).
On exit by selling: zero STT. If you sell your option back to the market (rather than letting it expire ITM), you pay no STT on the sale leg.
On auto-exercise at expiry (if ITM): 0.125% on FULL NOTIONAL VALUE. This is the gotcha. If NIFTY closes at 22,200 and your 22,000 CE auto-exercises, STT is 0.125% × 22,200 × 25 = ₹693. The intrinsic value you'd collect is 200 × 25 = ₹5,000 — minus ₹693 = ₹4,307 net. If the option was less ITM, the STT can exceed the intrinsic.
On entry (sell to open): 0.05% on the premium received. Same rate as buyer entry. Selling that 22,000 CE for ₹100 incurs ₹125 STT.
On exit by buying back: zero STT. Closing a short option position via a buy-to-cover does not incur STT on the close leg.
On expiry of OTM positions: zero STT. If your sold option expires worthless, you keep the premium and pay nothing more.
Net result: option sellers have slightly favourable STT mechanics overall because most sold options either expire OTM (zero STT on exit) or are closed early (zero STT on close).
Suppose you bought a NIFTY 22,000 CE for ₹50 on Wednesday. By Thursday morning, NIFTY is at 22,030 — your option is barely ITM, premium is around ₹35.
Option A: close the position. Sell at ₹35, lose ₹15 × 25 = ₹375 + entry STT ₹62.50. Net loss: about ₹437.
Option B: let it expire. If NIFTY settles at 22,030, you collect intrinsic of 30 × 25 = ₹750. But STT on auto-exercise = 0.125% × 22,030 × 25 = ₹688. Net collect: ₹62. Plus original entry STT of ₹62.50 and the ₹50 × 25 = ₹1,250 premium paid. Net loss: about ₹1,250.
Closing the position lost ₹437. Letting it expire ITM lost ₹1,250 — almost 3x worse despite ending up barely positive on intrinsic.
Run the math. Close at ₹35 (market): proceeds = 35 × 25 = ₹875, entry STT was ₹62.50, total recovered = ₹812.50. Hold to expiry: intrinsic = 30 × 25 = ₹750, exercise STT = 0.125% × 22,030 × 25 = ₹688, net = ₹62. Closing nets ₹750 more in this case. The barely-ITM trap eats deep-ITM-style STT regardless.
When intrinsic value is large enough that 0.125% × notional is a small fraction of the proceeds. Rule of thumb: if intrinsic > 1.5% of underlying price, auto-exercise STT is bearable. Below that, always close.
No. As an option seller, your STT was paid on entry (0.05% × premium received). Holding to OTM expiry triggers no further STT — the option just expires worthless and you keep the premium minus the original STT.
The estimate assumes today's spot. Actual STT on auto-exercise uses the official VWAP settlement price (3:00-3:30 PM IST), which can be ₹5-30 different from your estimate's spot. The STT is the 0.125% × settlement_price × lot — so a higher settlement price = higher STT.
Yes for entry and exit (0.05% on premium each side). For auto-exercise the rate is also 0.125% on notional, but stock options notional uses settlement price × lot size of the stock, which can be much larger than an index option's notional. So the trap is sharper for stock options.
Futures have their own STT structure (0.0125% on sell side only) and no auto-exercise STT trap, but they have unlimited loss potential and require much higher margin. The STT trap is solvable by closing ITM options before expiry — not a reason to avoid options entirely.