US vs India: what changes
The four wishes, theta, margin and payoffs are identical everywhere. What differs is the plumbing. This sheet lists every difference that changes a decision.
| Rule | NSE (India) | US (CBOE, OCC-cleared) |
|---|---|---|
| Exercise style | European: only at expiry, done by the exchange. | Stock and ETF options are American: the holder may exercise any day. Index options (SPX, NDX) are European. |
| Early assignment | Impossible. | Real. A short call on a stock going ex-dividend, or a deep ITM short put, can be assigned any night. |
| Contract size | Varies per underlying. NIFTY 65, stocks by lot. | Always 100 shares per contract for equities. |
| Strike ownership at expiry | Exchange auto-exercises every ITM option. | OCC "exercise by exception": auto-exercised if ITM by $0.01 or more. Holder can override by 5:30 pm ET. |
| Settlement, stock options | Physical delivery. ITM at expiry means shares move; brokers demand full margin in the last week. | Physical delivery, 100 shares per contract, T+1. |
| Settlement, index options | Cash. | Cash. SPX monthlies settle AM (opening print, third Friday). SPXW weeklies and dailies settle PM (4 pm close). |
| Expiry calendar | NIFTY weekly on Tuesday; monthly last Tuesday. One weekly index per exchange (SEBI, 2024). | SPX and major ETFs expire every trading day (0DTE). Stocks: Fridays, monthlies third Friday. |
| Margin for sellers | SPAN + exposure, set by the clearing corp, blocked upfront. Broker may add. | Reg T minimum: 20% of underlying + premium − OTM amount (min 10% of strike + premium). Portfolio margin for large accounts. Brokers add house margin. |
| Who may sell naked | Anyone with margin. No approval tiers. | Broker approval levels 1 to 4. Naked calls and puts need the top level. |
| Day-trading limits | None. | Pattern Day Trader $25k rule eliminated by SEC approval 14 Apr 2026, effective 4 Jun 2026; replaced by intraday margin standards, brokers have until Oct 2027 to implement. |
| Trading hours | 9:15 to 15:30 IST. No extended options session. | 9:30 to 16:00 ET; SPX and some ETFs trade nearly 24×5 in extended sessions. |
| Tax | Business income at slab rate. STT on sell side and on exercised ITM options. | Stock options: short/long-term capital gains. Index options (SPX, section 1256): 60% long-term, 40% short-term, whatever the holding period. |
| Quote unit | Premium per share, in ₹. | Premium per share, in $. Multiply by 100. |
What this means in practice
If you ever sell a US stock option, early assignment is the new thing to fear. In India you know you're safe until Tuesday. In the US a short call can be turned into short stock overnight, especially the day before a dividend.
0DTE is a US phenomenon. Because SPX expires every day and settles in cash, whole strategies exist around the last six hours of a contract's life. India has one weekly index expiry per exchange after SEBI's 2024 curbs.
Sizing is simpler in the US. Every contract is 100 shares. A $2.50 premium is $250. In India, 65 NIFTY units × ₹30 is one calculation, 250 Reliance × ₹30 another.
Sources: OIC on exercise by exception · FINRA 5:30 pm cut-off · Cboe SPX fact sheet · FINRA Notice 26-10 on the PDT change · Cboe margin manual · Varsity on physical settlement