Position Sizing in F&O Trading: A Practical Guide for Indian Traders

Why position sizing works differently in F&O

In equity markets, you choose how many shares to buy. In F&O, the unit is a lot — and NSE sets the lot size. You cannot buy half a Nifty lot. This means position sizing in derivatives often involves rounding to the nearest whole lot, which affects your exact risk per trade.

Current lot sizes (per NSE's derivatives specifications) — Nifty: 75 units per lot; Bank Nifty: 35 units per lot. These figures are revised periodically; always verify before calculating. The lot size multiplies your per-point gain or loss: a 100-point move in Bank Nifty with one lot = 100 × 35 = ₹3,500.

SEBI also mandates a minimum margin for every F&O position. This margin (SPAN plus exposure) must be maintained at all times, not just at trade entry. Your position size must account for whether your account holds enough margin to carry the trade through adverse intraday swings.

Three position sizing models

How it works: risk a fixed ₹ amount per trade regardless of account size or volatility · Best for: beginners who want simplicity · Limitation: does not scale with account growth; ignores volatility

How it works: risk a fixed % of total capital per trade (typically 1–2%) · Best for: most active traders; standard professional approach · Limitation: requires knowing your exact stop-loss distance before entry

How it works: adjust lot size based on how much the contract is moving (ATR or VIX) · Best for: experienced traders managing multiple positions · Limitation: more complex; requires a consistent measurement approach

The % of account model is the most practical for most Indian F&O traders. Risk 1% of your account per trade. On a ₹5,00,000 account, that is ₹5,000 at risk per trade. If Bank Nifty is at 50,000 and your stop-loss is 100 points below entry, the risk per lot is 100 × 35 = ₹3,500. You can trade one lot and stay within the 1% limit. Two lots = ₹7,000 risk — above the 1% rule.

{
  "type": "quiz",
  "slug": "position-sizing-1-percent-rule-quiz",
  "label": "QUIZ",
  "question": "Using the 1% rule on a ₹5,00,000 trading account, what is the maximum you should risk on a single trade?",
  "correctOptionKey": "B",
  "explanation": "1% of ₹5,00,000 = ₹5,000 — sized so that even 10 consecutive losses draw the account down only about 10%, leaving capital to trade through a drawdown.",
  "options": [
    {
      "key": "A",
      "text": "₹50,000 — 10% of the account"
    },
    {
      "key": "B",
      "text": "₹5,000 — 1% of total capital"
    },
    {
      "key": "C",
      "text": "₹500 — 0.1% of total capital"
    },
    {
      "key": "D",
      "text": "₹1,00,000 — whatever margin allows"
    }
  ]
}

Worked example: Bank Nifty with a stop-loss

Account size: ₹5,00,000. Risk per trade: 1% = ₹5,000.

Trade: Buy Bank Nifty futures at 50,000. Stop-loss at 49,800 (200 points below entry). Bank Nifty lot size: 35 units.

• Risk per lot: 200 points × 35 = ₹7,000
• Maximum lots allowed at 1% risk: ₹5,000 ÷ ₹7,000 = 0.71 lots → round down to 0 lots (can't trade this setup at 1% risk with this stop)
• To trade one lot: tighten the stop to 143 points (₹5,000 ÷ 35 = ₹142.86 per point)
• Alternatively, increase the risk tolerance to 1.4% (₹7,000) to accommodate one lot with a 200-point stop

The arithmetic forces a decision: take a tighter stop, raise the risk tolerance slightly, or skip the trade. All three are valid. What is not valid is ignoring the calculation and trading two or three lots because the setup "looks good."

What overleveraging looks like

A trader with a ₹5,00,000 account buys 5 lots of Nifty futures (margin required: roughly ₹2,80,000 at current SEBI margin rules). Nifty falls 150 points. Loss: 150 × 75 × 5 = ₹56,250 — more than 11% of the account on one trade. Three such trades in a week ends the account.

This is not an edge case. It is the pattern behind most F&O account blow-ups. SEBI's mandatory margin rules prevent the worst overleveraging at the broker level, but they do not prevent a trader from deploying the full allowed exposure on every position.

{
  "type": "quiz",
  "slug": "bank-nifty-lots-risk-quiz",
  "label": "QUIZ",
  "question": "You buy Bank Nifty futures at 50,000 with a 200-point stop-loss (lot size 35). At 1% risk on a ₹5,00,000 account, how many lots can you trade?",
  "correctOptionKey": "B",
  "explanation": "Risk per lot = 200 × 35 = ₹7,000, which exceeds the ₹5,000 (1%) limit — 0.71 lots rounds down to zero, so the trade needs a tighter stop, a slightly higher risk tolerance, or a pass.",
  "options": [
    {
      "key": "A",
      "text": "One lot — ₹7,000 of risk is close enough to the limit"
    },
    {
      "key": "B",
      "text": "Zero — risk per lot (₹7,000) exceeds the ₹5,000 limit, so tighten the stop or skip"
    },
    {
      "key": "C",
      "text": "Two lots — margin allows it"
    },
    {
      "key": "D",
      "text": "Five lots — the stop-loss makes lot count irrelevant"
    }
  ]
}

SEBI margin and position sizing

SEBI's margin framework requires every F&O position to be backed by SPAN margin (based on the strategy's risk profile) and exposure margin (a further buffer). For long options, margin is limited to the premium paid. For short options and futures, margin requirements are significantly higher and are updated by exchanges regularly.

Margin and position size interact: you might calculate that 3 lots fits your risk limit, but your account may not hold enough margin for 3 lots. Both constraints apply simultaneously. Always check your broker's margin calculator — or Sahi's position sizing tools — before placing the order.

The bottom line

Position sizing is the mechanical side of risk management — not the exciting part, but the part that keeps an account alive long enough for a strategy's edge to play out. The 1–2% risk rule is a starting point, not a ceiling carved in stone; the right number depends on your account size, the volatility of the instrument, and your stop-loss distance. What matters is that the number is calculated before entry, not after a trade goes wrong.

Related reads: Iron Condor and Multi-Leg Options Strategies in India · Trailing Stop-Loss: Meaning and How It Works · India VIX: The Volatility Index Explained · Trading Psychology and Risk Management