Almost every trader we speak to asks the same first question, and almost always in the same slightly embarrassed way: "how much money do I need to start?"
It is a good question. It is also the wrong shape. The honest answer is not one number — it is three: what one lot costs, what one loss costs, and what the exchange and the taxman take on the way in and out. Let us do all three, for SENSEX weekly options, with real arithmetic.
Your local kirana will happily sell you one kilo of atta or half a kilo. But eggs come on a tray, and the tray is the tray. You cannot walk out with seven.
Options work the same way. The exchange decides the tray size and calls it the lot size. For SENSEX weekly options on BSE, one lot is 20 quantity. You can buy one lot, or two, or thirteen. You cannot buy 7 quantity, and you cannot buy 25.
This single fact is why two traders looking at the same option can have wildly different money at risk. The option's price is per unit. Your bill is per lot.
As an option buyer, the sum is embarrassingly simple:
Premium × 20 = rupees that leave your account.
That is the whole thing. There is no separate margin to post, no mark-to-market call at 3 PM. You pay the premium, you own the option, and the most you can lose is exactly what you paid.
| Option premium | Cost of 1 lot | Cost of 5 lots |
|---|---|---|
| ₹100 | ₹2,000 | ₹10,000 |
| ₹200 | ₹4,000 | ₹20,000 |
| ₹300 | ₹6,000 | ₹30,000 |
| ₹400 | ₹8,000 | ₹40,000 |
| ₹500 | ₹10,000 | ₹50,000 |
Everything above is for buying. Selling options is a completely different animal financially. A seller does not pay a premium — they receive one, and in exchange they post margin with the exchange, because their loss is not capped at a known number.
That margin for a SENSEX weekly option typically runs well over a lakh of rupees per lot, and it is not a fixed figure — it recalculates with volatility, and it can be topped up intraday. This is why a ₹50,000 account that can comfortably buy several lots often cannot sell even one.
Here is where most retail sizing goes wrong. Traders ask "can I afford one lot?" The more useful question is "can I afford this loss twenty times in a row?"
Because you will have losing streaks. Everybody does. So the number that matters is not the cost of the lot — it is the cost of the stop-loss.
Our own machine uses a flat 22-point stop-loss on the option premium. Run that through the tray arithmetic:
Notice something: a ₹200 option and a ₹400 option cost very different amounts to buy, but with a fixed points-based stop they risk exactly the same rupees. That is not an accident. A stop measured in points is invariant to strike and premium, which makes losing days arithmetically predictable instead of emotionally surprising.
The premium is not the full bill. A round trip in F&O also carries brokerage, STT, exchange transaction charges, SEBI turnover fees, GST and stamp duty. Individually they look trivial. Together, on a small position taken several times a day, they are a real and permanent drag.
Think of it as the auto-rickshaw meter's minimum charge. It does not care that your ride was short. Take twenty short rides and the minimum charges alone become the fare.
We are not going to hand you a magic figure, because there isn't one and anyone who gives you one is selling something. What we can do is show you the shape of the answer:
And since we report our own book plainly: September opened badly for us. The first session of the month closed at −₹19,350, and the second session produced no trades at all because nothing cleared our entry conditions. That is what the arithmetic above looks like when it goes against you, and it is exactly why we size off the stop rather than off the account balance.
Get the tray arithmetic right first. Everything else in this business is downstream of it.