F&O Margin Calculator

How to read your margin estimate

Figures below are illustrative, using the tool’s default Nifty example and the normal-volatility rates last reviewed 1 September 2026.

What the number actually means

When you buy an option you pay a premium, and that premium is the most you can lose, so the exchange asks for nothing more. When you sell (write) an option or trade a future, your loss is open-ended, so the exchange makes you park collateral up front. That collateral is the margin.

The margin has two parts:

• SPAN margin is the exchange’s model (Standard Portfolio Analysis of Risk) of the worst realistic one-day loss on your position. It is the bulk of the number.
• Exposure margin is a flat extra buffer on top of SPAN, for gaps the model doesn’t capture.

Add them and you get the total a broker blocks for as long as the position is open. It is not a fee. You get it back when you exit, but it is capital you can’t use for anything else meanwhile.

A worked example (the numbers this tool shows)

Take the default: sell one lot of Nifty with the index at 24,850 and a lot size of 65.

That is about ₹1.45 lakh to carry a single lot. If you sold that option for, say, ₹120 a unit you would also receive ₹7,800 in premium (120 × 65) as a credit, but that cash does not reduce the margin blocked; it simply lands in your account while the ₹1.45 lakh stays locked.

Now hedge it. Buy a further option 200 points away and your maximum loss is capped, so the exchange blocks roughly that capped loss (order of ₹9,000 to ₹13,000) instead of the full ₹1.45 lakh: the same view for a fraction of the capital. That is why defined-risk spreads are the standard way retail sellers control margin.

Why your broker’s number won’t match exactly

This calculator uses simplified, normal-volatility rates. The exchange’s live SPAN engine does not, and that is the honest reason the figures differ:

• SPAN is recalculated several times a day. The rate that gave ₹1.45 lakh this morning can be higher this afternoon if volatility ticks up.
• It is strike- and portfolio-aware. Real SPAN prices each specific strike and nets off offsetting positions in your account; a flat percentage can’t.
• Brokers add their own cushion. Many block a little over the exchange minimum to protect against intraday spikes.

Treat this as a planning estimate for how much capital you need to carry a position, and always confirm the exact figure in your broker’s official margin calculator before you place the order.

What moves the margin up or down

• Volatility. The single biggest driver. Higher India VIX means higher SPAN; margins routinely jump 20 to 40% around results season, budget day, RBI policy and elections.
• Spot level. Margin is a percentage of contract value, so as Nifty rises the rupee margin rises with it.
• Lots. It scales linearly; five lots is five times one lot.
• Hedging. Buying a protective leg is the one lever that cuts margin sharply, because it caps the modelled loss.
• Product. Futures and option-selling carry margin; option-buying carries none.

Mistakes people make reading it

• Treating margin as the cost of the trade. It isn’t: it is blocked collateral you get back. Your real cost is brokerage, STT and other charges (see the brokerage calculator), plus any loss.
• Sizing to the exact margin. If ₹1.45 lakh is blocked and you hold ₹1.5 lakh, one volatile morning can trigger a margin shortfall and a penalty. Many traders keep 1.3 to 1.5 times the shown margin free. See how much capital you need.
• Forgetting margin rises after you’re in. The figure at entry is not fixed; a sharp move against you increases it, and brokers can square you off if you can’t top up.
• Assuming the premium reduces the margin. It doesn’t. Received premium is separate cash; the full margin stays blocked until you exit.
• Ignoring the event calendar. Selling naked options into an event on “normal” margin is how accounts blow up when the exchange doubles SPAN overnight.