Position Sizing — Risk First, Size Second
How to size an F&O trade from the risk you'll accept, and why SEBI's larger contract sizes make disciplined sizing harder for small accounts.
Most traders pick a direction first and a size second — usually 'how many lots can I afford.' That's backwards. Professional sizing starts from the risk you're willing to lose on the trade, and derives the size from it. Get this one habit right and you survive long enough for your edge to matter.
This chapter covers risk-first sizing, the arithmetic that turns a risk budget into a position size, and the specific problem SEBI's larger F&O contracts create for small accounts.
Risk first: the 1-2% rule
The core discipline: risk a small, fixed fraction of capital per trade — commonly 1-2%. On a ₹10 lakh account, 1% is ₹10,000 of loss if the stop is hit. Not 1% of the position — 1% of capital, as the actual rupee loss when you're stopped out.
Why so small: it lets you survive a losing streak. At 2% risk, ten straight losers costs roughly 18-20% — painful but recoverable. At 10% risk, ten losers can end the account. The fraction is a survival parameter, not a timidity setting.
From risk budget to position size
Futures / stock: position size = risk budget ÷ (stop distance × lot size). If you'll risk ₹10,000 and your stop is ₹20 away on a stock with a 250-share lot, that's ₹10,000 ÷ (20 × 250) = 2 lots. The stop distance, not your conviction, sets the size.
Long options: the premium paid is the natural maximum loss, so a clean approach is to risk only the premium you can afford to lose entirely — size so total premium ≤ your risk budget. (Don't actually let it ride to zero, but cap the bet there.)
Short options: loss is open-ended, so you must size off a defined stop on the underlying, not the premium collected — the premium is what you can make, not what you can lose.
The Rs 15 lakh problem
SEBI raised the minimum index-derivatives contract value to about ₹15 lakh (from ₹5-7 lakh) in November 2024, and lot sizes rose with it. The consequence for sizing: one index lot now commits a large notional, so a single NIFTY or BANK NIFTY lot can blow straight past a 2% risk budget on a small account — there's no 'fractional lot' to scale down to.
Practically: small accounts often cannot size index F&O properly at all, and forcing a lot anyway means over-risking. The honest options are to trade defined-risk option spreads (which cap and shrink the risk per lot), trade smaller-notional stock options, or simply not trade index F&O until the account supports one lot inside the risk budget. The upfront-premium rule (since Feb 2025) also ended the old trick of controlling large option positions with tiny margin.
Common misreads
- Sizing by 'how many lots can I afford' instead of 'how much will I lose if stopped'.
- Risking 1-2% of the position rather than 1-2% of capital — a much bigger bet than intended.
- Forcing an index lot on a small account post-2024 — one lot can blow the whole risk budget.
Key takeaways
- Size from risk, not affordability: fix the rupee loss per trade at ~1-2% of capital.
- 1% of CAPITAL as the loss when stopped — not 1% of position size.
- Futures/stock: size = risk budget ÷ (stop distance × lot size). Stop distance sets size, not conviction.
- Long options: cap total premium at the risk budget; short options: size off an underlying stop (loss is open-ended).
- SEBI's ~Rs 15 lakh min contract (Nov 2024) means one index lot can exceed a small account's 2% budget — use spreads or smaller instruments.
Sizing an F&O position
What does the 2% rule actually mean?
Risk no more than ~2% of your total trading capital on any single trade — measured as the actual rupee loss if your stop is hit, not 2% of the position's notional. On ₹10 lakh, that's ₹20,000 of loss per trade. The point is survival: it keeps a losing streak from ending the account, so your edge has time to play out.
How do I convert a risk budget into a number of lots?
For futures or stock: lots = risk budget ÷ (stop distance × lot size). Risk ₹10,000 with a ₹20 stop on a 250-share lot → ₹10,000 ÷ (20 × 250) = 2 lots. The stop distance and lot size determine the size; your conviction does not. A wider stop means a smaller position for the same risk.
How is sizing different for buying vs selling options?
When you buy options, the premium is your maximum loss, so size such that the total premium you pay stays within your risk budget. When you sell options, the loss is open-ended, so you must size off a defined stop on the underlying — the premium collected is your potential gain, not your risk. Treating collected premium as 'the risk' is how option sellers blow up.
Why is it hard to size index F&O on a small account now?
Because SEBI raised the minimum index-derivatives contract value to roughly ₹15 lakh in November 2024 and lot sizes increased. One NIFTY or BANK NIFTY lot now carries a large notional, so the loss on a single lot can exceed a 2% risk budget on a small account — and you can't trade a fraction of a lot. The fix is defined-risk spreads, smaller-notional stock options, or waiting until the account is large enough.
Did SEBI's rules change how much margin I need to buy options?
Yes. Since February 2025, option premium must be collected upfront from buyers, which ended the practice of controlling a large option position with only a small amount in the account. Combined with the larger contract sizes, it means index F&O now requires meaningfully more capital to trade within sane risk limits.