Underlying
The index, stock, or commodity whose price behaviour drives every tick of a futures or options contract written on it.
Definition
The underlying is the financial instrument — an equity index, individual stock, commodity, currency pair, or interest-rate benchmark — upon which a derivative contract is written and whose price movements entirely determine the derivative's payoff at settlement. In Indian equity derivatives, the two dominant underlyings are the Nifty 50 index and the Bank Nifty index, both computed in real time by NSE from the prices of their constituent stocks. SEBI prescribes the criteria — minimum average daily turnover, market capitalisation, and median quarter-sigma order size — that a stock must meet before NSE can list futures and options on it.
Why it matters
Understanding which underlying you are trading is foundational because each underlying has its own liquidity profile, lot size, expiry calendar, margin framework, and settlement mechanism. Index underlyings such as Nifty 50 and Bank Nifty settle in cash — there is no physical delivery of shares. Stock underlyings, by contrast, are subject to compulsory physical delivery on NSE for in-the-money positions at expiry, which creates distinct margin and logistics requirements near the delivery period. The underlying also determines which exchange hosts the most liquid contracts: Nifty options trade almost exclusively on NSE, while Sensex and Bankex options trade on BSE. Confusing the exchange or the underlying can result in mismatched hedges or unintended position exposure.
How it works
The price of every derivative — whether a futures contract or an option's intrinsic component — is derived from the live spot price of the underlying via the cost-of-carry model (for futures) or option pricing models such as Black-Scholes (for options). As the underlying moves, all derived contracts reprice: call premiums rise when the underlying rises, put premiums rise when the underlying falls. SEBI periodically reviews the F&O-eligible stock list and removes underlyings that no longer meet liquidity thresholds; positions in de-listed F&O stocks must be closed before the last contract expiry date. Currently, around 180–200 individual stocks have active futures and options alongside nine index underlyings on NSE and BSE combined.
Example
Suppose you buy a 24,200 call option with Nifty 50 as the underlying. If Nifty (the underlying) rises from 24,000 to 24,500, your call moves deep in-the-money and accrues substantial intrinsic value. If Nifty instead falls to 23,700, your call expires worthless regardless of how any individual stock in the Nifty basket performed. Now contrast this with a stock option — say you buy an HDFC Bank 1,800 CE. Here, HDFC Bank's individual share price (not Nifty) is the underlying, and only HDFC Bank's move determines your payoff. This highlights why identifying the correct underlying and monitoring its specific drivers (earnings, RBI policy for Bank Nifty, global indices for Nifty) is step one of any option trade plan.
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