Option Selling Margins: How NSE SPAN + Exposure Margins Work
The complete guide to margin requirements for writing options on NSE — SPAN margin, exposure margin, how they are computed, and why the premium received is not your only capital.
Why Selling Options Requires More Capital Than Buying
When you buy an option, your maximum loss is the premium you paid. Your broker blocks only that premium as margin. When you sell an option, your risk is that the option moves deep against you, and your maximum loss can be substantially larger than the premium you collected. To protect the clearing house, the exchange requires sellers to post margin that covers the potential loss.
This is why the Options Sell Calculator asks for margin per lot, not just premium. On NSE, an out-of-the-money Nifty option seller might need 60,000–90,000 rupees per lot of margin, while the premium collected on the same option is only a few thousand rupees.
SPAN Margin: The Main Component
The SPAN (Standard Portfolio Analysis of Risk) margin is computed by the clearing corporation using a sophisticated risk model. It runs thousands of hypothetical market scenarios — combining moves in the underlying, changes in volatility, and shifts in time to expiry — and blocks the worst-case loss among them, with a small buffer.
SPAN margin is portfolio-based: it recognises that a covered position or a spread reduces risk. Selling a call and buying a further out-of-the-money call costs less margin than selling the call naked, because the long option caps the loss. Selling options on both sides of the market — a strangle — gets a partial offset because both sides rarely lose at once.
Exposure Margin: The Second Component
On top of SPAN, exchanges add an exposure margin, which is a fixed percentage of the contract value. For Nifty options, the exposure margin is typically about 3% of the notional value of the underlying. It acts as an additional buffer against gap moves and volatility that the risk scenarios might underweight.
The total margin requirement for a seller is SPAN margin plus exposure margin. Because contract value changes as the underlying moves, the margin requirement also changes daily — brokers re-block and release margin as your position's risk changes.
How the Margin Number Depends on the Option You Sell
The margin is not a fixed per-lot number. It depends on three things: the strike price relative to the spot (how far in or out of the money), the time to expiry, and the implied volatility. A near-the-money option with three weeks to expiry carries a higher margin than a deep out-of-the-money option expiring in a few days.
As the underlying moves towards your strike, margin rises; as it moves away, margin falls. When you square off or the option expires, the margin is released. This dynamic is why experienced option writers keep a margin buffer — a naked position that used 90% of your available margin is one sharp move away from a margin call.
The True Economics of Option Selling
The premium you receive is the maximum profit, and it is collected upfront. Against that, you block margin that could have earned interest or funded other trades. The profit-on-margin percentage matters: collecting a 1,200-rupee premium on 75,000 rupees of blocked margin is a 1.6% return over the holding period, not an impressive number once you annualise it.
The Options Sell Calculator shows this trade-off directly — max lots from available margin, total premium income, the stop-loss loss, and the reward-to-risk ratio. Because the maximum gain is capped but the loss can be many times the premium, disciplined stop losses and correct position sizing are what separate profitable option writers from occasional blow-ups.
Practical Guidance for New Option Sellers
Start by calculating your worst-case loss at a realistic stop-loss level before you enter the trade — the calculator does this for you. Never allocate more than a portion of your margin to a single naked position, and always keep a buffer for intraday margin spikes. Prefer strategies that reduce margin, such as spreads or covered writes, while you learn.
Finally, verify the exact margin figure from your broker's margin dashboard before placing the trade. The default of 65,000 rupees per Nifty lot in the calculator is an estimate; the actual number moves with market conditions and your exact strike and expiry.
About the Author
The FinCalc Pro editorial team researches Indian personal finance tools and regulations to explain them with clear, accurate math.