Six or seven articles on this site mention margin in passing — the amount blocked, the shortfall penalty, the way it rises through expiry week. None of them explain it, because each one was about something else. This is the page they should have been pointing at.
Margin is where most derivative accounts get into trouble, and almost never because somebody was wrong about direction.
Margin is collateral, not the price of the position
Start here, because nearly every expensive misunderstanding descends from this one.
When you buy a share for ten thousand rupees, that is the transaction. Ten thousand leaves your account, a holding appears, and the worst case is that it becomes worth nothing. Your maximum loss is the amount you spent, and it is known the moment you press the button.
A futures position is not a purchase. Nothing has been bought and nothing has been paid for. You have entered an obligation to settle a difference later, and the exchange blocks an amount of your money as security that you will be good for that difference. The blocked amount is collateral. It is not a payment, it is not the cost, and it is not a limit on what you can lose.
A contract with a value of eight lakh rupees might block around a lakh. If the underlying moves twenty percent against you, the loss is around a lakh and sixty thousand — more than was blocked, and the balance is owed. That is the whole of leverage, described without the word.
The same logic applies to selling an option. The premium arrives in your account, which feels like income, and the margin is blocked against a loss that has no defined ceiling. Buying an option is the one case that behaves like a purchase: you pay the premium, no margin is blocked, and the premium is genuinely the most you can lose.
SPAN and exposure, in plain terms
The blocked amount arrives in two pieces, and knowing which is which explains why the number moves when nothing appears to have happened.
SPAN margin is the exchange's estimate of the worst single-day loss your position could suffer, produced by running it through a range of price and volatility scenarios. It is not a fixed percentage. When markets get volatile, the scenarios get wider, and the SPAN figure on a position you have not touched goes up on its own. People discover this on the days they can least afford to.
Exposure margin sits on top as an additional cushion, calculated on the contract value rather than on scenarios. It is steadier than SPAN and it is what makes the total meaningfully larger than the risk model alone would demand.
Two consequences worth internalising. First, a hedged position blocks far less than two separate positions would, because the risk model can see that one leg protects the other — this is the single largest practical argument for defined-risk structures and it shows up directly in what you can afford to hold. Second, the requirement is recalculated continuously, so a quiet week can raise your blocked amount purely because volatility rose somewhere.
Peak margin, and why a snapshot matters
This one catches people who are certain they did nothing wrong, and the reason is that the check is not performed when you think it is.
Compliance with the requirement is not measured at the end of the day. Random snapshots are taken through the session, and your account has to be adequately funded at each of those moments. An account that was short of the requirement for twenty minutes in the middle of the afternoon and comfortable by close has still been short, and the record says so.
The practical effect is that intraday leverage of the sort that used to be advertised no longer exists in the way people remember. You need the full requirement upfront, not by evening.
Where this bites in ordinary use: you place a second position assuming the first one's release has already reflected, or you rely on the sale proceeds of something sold that morning. Funds from a sale are not immediately available as margin in every case, and a snapshot taken in the gap finds a shortfall that you never intended and did not see.
What happens when it runs short
Three separate things, and they arrive in an order that surprises people.
A penalty is levied. The exchange charges for a shortfall, as a percentage of the amount short, and the rate steps up with size and with repetition within a month. It is not a rounding error and it is deducted from your account without anybody asking.
Your broker acts, on their timetable rather than yours. If the account is short and you do not fund it, positions get squared off — and this is where being unavailable during market hours turns into an expensive habit. The square-off happens at whatever price exists at that moment, which by definition is a moment when the market has already moved against you.
The order matters here and people get it backwards: the broker is not obliged to wait for you, notify you successfully, or choose the position you would have chosen. Their exposure is being managed, not yours.
Losses settle daily. Futures are marked to market each evening: an adverse day is debited from your account that night rather than accumulating quietly until you exit. So the requirement can rise and your balance can fall on the same day, from the same move, which is how an account that looked comfortable on Monday is short on Wednesday without a single new position.
The defence is unexciting and it works. Hold a genuine buffer above the requirement rather than the exact figure, size positions against the buffer, and never treat the blocked amount as though it were the risk.
Pledging shares, and the trap inside it
Holdings can be pledged to generate collateral, which lets existing investments support a derivative position instead of leaving cash idle. It is a legitimate arrangement and it carries a specific danger that is easy to miss.
A haircut is applied, so shares worth a lakh might yield seventy or eighty thousand of collateral depending on the security. Brokers also require a portion of the requirement to be met in actual cash rather than entirely through pledged securities, so the arrangement never covers the whole of it.
Here is the part that hurts. Pledged shares have not stopped being shares. In a broad fall, the market goes down, your position loses money, and the collateral supporting it shrinks at the same time — three things moving against you at once, driven by the same event. An arrangement that looked comfortable in a calm month can unwind quickly, and the forced sale of the pledged holding is the outcome people never modelled.
If you use this route, take less collateral than you are offered, and keep enough cash that a fall in your holdings does not by itself create a shortfall.
The short version
Margin is security you post, not a payment you make, and it does not cap your loss. It is computed as a risk estimate plus a cushion, and it rises on its own when volatility rises. It is checked at random moments during the session rather than at the close. Falling short costs a penalty and hands the timing of your exit to somebody else. And funding it with pledged shares links your collateral to the same market that is moving your position.
Everything above is mechanics rather than strategy, and mechanics is the part that decides whether an account survives long enough for strategy to matter. Futures, Options & Derivatives Mastery covers this material in sequence, with the position structures that follow from it — enrolment at study.thefinbaba.com, Rs 10,000.
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Rates, haircuts and penalty slabs are set by the exchanges and brokers and are revised periodically — verify current figures with your own broker before relying on any number here. This is educational material, not advice. We run no tips group and no signal service, we manage nobody's money, and no return is promised. Derivatives can lose more than the amount blocked against them.
Disclosure: the account-opening link on this page is under Atul Shrivastava's Zerodha Authorised Person registration (NSE AP Reg: AP2516003481; Zerodha Broking Ltd. SEBI Reg: INZ000031633) and earns a revenue share. TheFinBaba is not a SEBI-registered Investment Adviser — this content is educational, not investment advice.
Frequently Asked Questions
Is margin the maximum I can lose?
No, and this is the most expensive misunderstanding in derivatives. The blocked amount is security you post, not the cost of the position. A futures position or a sold option can lose more than the amount blocked against it, and the difference is owed. Only buying an option limits the loss to what you paid.
Why did my blocked amount increase without me doing anything?
SPAN is recalculated from volatility scenarios rather than fixed as a percentage, so when markets get more volatile the requirement on an untouched position rises. Exchanges also raise requirements ahead of events and through expiry week on stock derivatives, where physical settlement is possible.
What is the penalty for a shortfall?
The exchange levies a charge as a percentage of the amount short, stepping up with the size of the shortfall and with repeat instances in the same month. Your broker may also square off positions to bring the account back into line. Current slabs are published by the exchanges and are worth checking directly.
Does hedging reduce the amount blocked?
Substantially, yes. The risk model can see that one leg limits the loss on the other, so a spread blocks far less than the two positions would separately. This is a real practical argument for defined-risk structures, and it shows up immediately in how much of your account a position consumes.
Can I use my shares instead of cash?
Partly. Pledging holdings generates collateral after a haircut, and brokers require some portion of the requirement in cash regardless. The risk to understand is that a market fall reduces your position value and your collateral value at the same time, from the same move, which is how these arrangements unwind quickly.
Related Reading
- F&O Mastery - the full module list
- Where futures and options differ
- Why requirements rise through expiry week
- Using futures to reduce an exposure
- Two short structures compared
- What the tax return needs from you
Disclaimer: TheFinBaba provides educational content only - this is not investment advice. Trading involves risk of loss.
